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 $62.44   5.868%   $66.104   $66.10   $66.10   $66.10  
  Purchase #2 $182.65   13.154%   $206.6758   $206.68   $206.70   $206.70  
  Purchase #3 $249.71   4.170%   $260.1229   $260.12   $260.10   $260.10  
  Purchase #4 $147.46   3.189%   $152.1625   $152.16   $152.15   $152.20  
  Purchase #5 $149.83   11.133%   $166.5106   $166.51   $166.50   $166.50  
  Purchase #6 $53.88   5.821%   $57.0164   $57.02   $57.00   $57.00  
  Purchase #7 $147.27   11.512%   $164.2237   $164.22   $164.20   $164.20  
  7 purchase totals = $993.24       $1,072.8159   $1,072.81   $1,072.75   $1,072.80