Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $190.34   13.816%   $216.6374   $216.64   $216.65   $216.60  
  Purchase #2 $160.94   10.372%   $177.6327   $177.63   $177.65   $177.60  
  Purchase #3 $105.70   11.555%   $117.9136   $117.91   $117.90   $117.90  
  Purchase #4 $218.62   9.385%   $239.1375   $239.14   $239.15   $239.10  
  Purchase #5 $141.66   13.861%   $161.2955   $161.30   $161.30   $161.30  
  Purchase #6 $125.25   10.166%   $137.9829   $137.98   $138.00   $138.00  
  Purchase #7 $202.43   9.823%   $222.3147   $222.31   $222.30   $222.30  
  7 purchase totals = $1,144.94       $1,272.9143   $1,272.91   $1,272.95   $1,272.80