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 $175.69   11.312%   $195.5641   $195.56   $195.55   $195.60  
  Purchase #2 $32.83   5.573%   $34.6596   $34.66   $34.65   $34.70  
  Purchase #3 $126.63   5.663%   $133.8011   $133.80   $133.80   $133.80  
  Purchase #4 $238.67   11.775%   $266.7734   $266.77   $266.75   $266.80  
  Purchase #5 $83.61   10.637%   $92.5036   $92.50   $92.50   $92.50  
  Purchase #6 $169.92   8.285%   $183.9979   $184.00   $184.00   $184.00  
  Purchase #7 $104.53   11.810%   $116.875   $116.88   $116.90   $116.90  
  7 purchase totals = $931.88       $1,024.1747   $1,024.17   $1,024.15   $1,024.30