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 $165.62   6.641%   $176.6188   $176.62   $176.60   $176.60  
  Purchase #2 $106.94   11.779%   $119.5365   $119.54   $119.55   $119.50  
  Purchase #3 $104.25   10.782%   $115.4902   $115.49   $115.50   $115.50  
  Purchase #4 $208.79   9.817%   $229.2869   $229.29   $229.30   $229.30  
  Purchase #5 $115.89   9.569%   $126.9795   $126.98   $127.00   $127.00  
  Purchase #6 $54.96   13.685%   $62.4813   $62.48   $62.50   $62.50  
  Purchase #7 $249.85   13.357%   $283.2225   $283.22   $283.20   $283.20  
  7 purchase totals = $1,006.30       $1,113.6157   $1,113.62   $1,113.65   $1,113.60