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 $161.62   3.297%   $166.9486   $166.95   $166.95   $166.90  
  Purchase #2 $216.61   10.755%   $239.9064   $239.91   $239.90   $239.90  
  Purchase #3 $89.98   7.624%   $96.8401   $96.84   $96.85   $96.80  
  Purchase #4 $55.90   12.557%   $62.9194   $62.92   $62.90   $62.90  
  Purchase #5 $246.26   6.793%   $262.9884   $262.99   $263.00   $263.00  
  Purchase #6 $193.49   4.816%   $202.8085   $202.81   $202.80   $202.80  
  Purchase #7 $55.41   11.176%   $61.6026   $61.60   $61.60   $61.60  
  7 purchase totals = $1,019.27       $1,094.0140   $1,094.02   $1,094.00   $1,093.90