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 $59.99   3.873%   $62.3134   $62.31   $62.30   $62.30  
  Purchase #2 $149.53   11.533%   $166.7753   $166.78   $166.80   $166.80  
  Purchase #3 $54.51   4.315%   $56.8621   $56.86   $56.85   $56.90  
  Purchase #4 $241.50   3.567%   $250.1143   $250.11   $250.10   $250.10  
  Purchase #5 $120.43   4.166%   $125.4471   $125.45   $125.45   $125.40  
  Purchase #6 $208.90   12.373%   $234.7472   $234.75   $234.75   $234.70  
  Purchase #7 $122.63   10.796%   $135.8691   $135.87   $135.85   $135.90  
  7 purchase totals = $957.49       $1,032.1285   $1,032.13   $1,032.10   $1,032.10