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 $41.87   10.142%   $46.1165   $46.12   $46.10   $46.10  
  Purchase #2 $66.67   11.474%   $74.3197   $74.32   $74.30   $74.30  
  Purchase #3 $235.27   6.240%   $249.9508   $249.95   $249.95   $250.00  
  Purchase #4 $226.43   7.552%   $243.53   $243.53   $243.55   $243.50  
  Purchase #5 $179.99   9.644%   $197.3482   $197.35   $197.35   $197.30  
  Purchase #6 $109.32   13.231%   $123.7841   $123.78   $123.80   $123.80  
  Purchase #7 $109.27   5.205%   $114.9575   $114.96   $114.95   $115.00  
  7 purchase totals = $968.82       $1,050.0068   $1,050.01   $1,050.00   $1,050.00