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 $62.80   5.756%   $66.4148   $66.41   $66.40   $66.40  
  Purchase #2 $240.66   9.553%   $263.6502   $263.65   $263.65   $263.70  
  Purchase #3 $117.90   12.272%   $132.3687   $132.37   $132.35   $132.40  
  Purchase #4 $118.53   5.229%   $124.7279   $124.73   $124.75   $124.70  
  Purchase #5 $220.73   10.535%   $243.9839   $243.98   $244.00   $244.00  
  Purchase #6 $48.87   6.421%   $52.0079   $52.01   $52.00   $52.00  
  Purchase #7 $159.42   13.248%   $180.54   $180.54   $180.55   $180.50  
  7 purchase totals = $968.91       $1,063.6934   $1,063.69   $1,063.70   $1,063.70