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 $30.45   10.307%   $33.5885   $33.59   $33.60   $33.60  
  Purchase #2 $240.99   6.581%   $256.8496   $256.85   $256.85   $256.80  
  Purchase #3 $26.37   3.180%   $27.2086   $27.21   $27.20   $27.20  
  Purchase #4 $64.55   9.359%   $70.5912   $70.59   $70.60   $70.60  
  Purchase #5 $113.78   10.862%   $126.1388   $126.14   $126.15   $126.10  
  Purchase #6 $128.27   4.567%   $134.1281   $134.13   $134.15   $134.10  
  Purchase #7 $244.76   13.473%   $277.7365   $277.74   $277.75   $277.70  
  7 purchase totals = $849.17       $926.2413   $926.25   $926.30   $926.10