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 $43.80   11.828%   $48.9807   $48.98   $49.00   $49.00  
  Purchase #2 $242.32   6.701%   $258.5579   $258.56   $258.55   $258.60  
  Purchase #3 $243.26   4.239%   $253.5718   $253.57   $253.55   $253.60  
  Purchase #4 $22.81   10.234%   $25.1444   $25.14   $25.15   $25.10  
  Purchase #5 $154.86   9.120%   $168.9832   $168.98   $169.00   $169.00  
  Purchase #6 $224.29   9.871%   $246.4297   $246.43   $246.45   $246.40  
  Purchase #7 $236.45   7.551%   $254.3043   $254.30   $254.30   $254.30  
  7 purchase totals = $1,167.79       $1,255.9720   $1,255.96   $1,256.00   $1,256.00