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 $62.57   4.702%   $65.512   $65.51   $65.50   $65.50  
  Purchase #2 $97.89   12.544%   $110.1693   $110.17   $110.15   $110.20  
  Purchase #3 $82.92   11.252%   $92.2502   $92.25   $92.25   $92.30  
  Purchase #4 $250.65   10.468%   $276.888   $276.89   $276.90   $276.90  
  Purchase #5 $29.68   13.264%   $33.6168   $33.62   $33.60   $33.60  
  Purchase #6 $227.84   7.441%   $244.7936   $244.79   $244.80   $244.80  
  Purchase #7 $241.59   7.769%   $260.3591   $260.36   $260.35   $260.40  
  7 purchase totals = $993.14       $1,083.5890   $1,083.59   $1,083.55   $1,083.70