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 $247.97   5.860%   $262.501   $262.50   $262.50   $262.50  
  Purchase #2 $39.54   3.405%   $40.8863   $40.89   $40.90   $40.90  
  Purchase #3 $10.42   5.560%   $10.9994   $11.00   $11.00   $11.00  
  Purchase #4 $195.80   3.379%   $202.4161   $202.42   $202.40   $202.40  
  Purchase #5 $102.46   9.684%   $112.3822   $112.38   $112.40   $112.40  
  Purchase #6 $131.42   6.262%   $139.6495   $139.65   $139.65   $139.60  
  Purchase #7 $241.50   11.168%   $268.4707   $268.47   $268.45   $268.50  
  7 purchase totals = $969.11       $1,037.3052   $1,037.31   $1,037.30   $1,037.30