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 $53.40   13.197%   $60.4472   $60.45   $60.45   $60.40  
  Purchase #2 $223.57   11.229%   $248.6747   $248.67   $248.65   $248.70  
  Purchase #3 $126.29   6.486%   $134.4812   $134.48   $134.50   $134.50  
  Purchase #4 $79.66   6.128%   $84.5416   $84.54   $84.55   $84.50  
  Purchase #5 $54.88   5.686%   $58.0005   $58.00   $58.00   $58.00  
  Purchase #6 $186.48   4.858%   $195.5392   $195.54   $195.55   $195.50  
  Purchase #7 $153.80   3.859%   $159.7351   $159.74   $159.75   $159.70  
  7 purchase totals = $878.08       $941.4195   $941.42   $941.45   $941.30