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 $110.53   8.154%   $119.5426   $119.54   $119.55   $119.50  
  Purchase #2 $61.48   10.623%   $68.011   $68.01   $68.00   $68.00  
  Purchase #3 $9.25   3.799%   $9.6014   $9.60   $9.60   $9.60  
  Purchase #4 $134.89   13.495%   $153.0934   $153.09   $153.10   $153.10  
  Purchase #5 $205.45   6.302%   $218.3975   $218.40   $218.40   $218.40  
  Purchase #6 $143.69   4.572%   $150.2595   $150.26   $150.25   $150.30  
  Purchase #7 $248.28   3.343%   $256.58   $256.58   $256.60   $256.60  
  7 purchase totals = $913.57       $975.4854   $975.48   $975.50   $975.50