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 $89.58   13.316%   $101.5085   $101.51   $101.50   $101.50  
  Purchase #2 $127.31   10.413%   $140.5668   $140.57   $140.55   $140.60  
  Purchase #3 $221.88   8.759%   $241.3145   $241.31   $241.30   $241.30  
  Purchase #4 $124.43   9.406%   $136.1339   $136.13   $136.15   $136.10  
  Purchase #5 $236.44   3.826%   $245.4862   $245.49   $245.50   $245.50  
  Purchase #6 $59.86   3.568%   $61.9958   $62.00   $62.00   $62.00  
  Purchase #7 $105.47   10.712%   $116.7679   $116.77   $116.75   $116.80  
  7 purchase totals = $964.97       $1,043.7736   $1,043.78   $1,043.75   $1,043.80