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 $224.84   13.867%   $256.0186   $256.02   $256.00   $256.00  
  Purchase #2 $209.79   3.522%   $217.1788   $217.18   $217.20   $217.20  
  Purchase #3 $150.36   12.683%   $169.4302   $169.43   $169.45   $169.40  
  Purchase #4 $206.29   4.706%   $215.998   $216.00   $216.00   $216.00  
  Purchase #5 $198.99   13.247%   $225.3502   $225.35   $225.35   $225.40  
  Purchase #6 $24.68   3.443%   $25.5297   $25.53   $25.55   $25.50  
  Purchase #7 $114.58   9.651%   $125.6381   $125.64   $125.65   $125.60  
  7 purchase totals = $1,129.53       $1,235.1436   $1,235.15   $1,235.20   $1,235.10