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 $129.58   10.592%   $143.3051   $143.31   $143.30   $143.30  
  Purchase #2 $173.63   9.685%   $190.4461   $190.45   $190.45   $190.40  
  Purchase #3 $65.53   13.202%   $74.1813   $74.18   $74.20   $74.20  
  Purchase #4 $149.75   9.344%   $163.7426   $163.74   $163.75   $163.70  
  Purchase #5 $9.74   5.143%   $10.2409   $10.24   $10.25   $10.20  
  Purchase #6 $203.80   5.598%   $215.2087   $215.21   $215.20   $215.20  
  Purchase #7 $155.88   6.575%   $166.1291   $166.13   $166.15   $166.10  
  7 purchase totals = $887.91       $963.2538   $963.26   $963.30   $963.10