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 $241.90   8.616%   $262.7421   $262.74   $262.75   $262.70  
  Purchase #2 $107.52   4.751%   $112.6283   $112.63   $112.65   $112.60  
  Purchase #3 $104.68   6.494%   $111.4779   $111.48   $111.50   $111.50  
  Purchase #4 $129.44   4.613%   $135.4111   $135.41   $135.40   $135.40  
  Purchase #5 $153.62   11.790%   $171.7318   $171.73   $171.75   $171.70  
  Purchase #6 $118.39   7.186%   $126.8975   $126.90   $126.90   $126.90  
  Purchase #7 $87.36   5.350%   $92.0338   $92.03   $92.05   $92.00  
  7 purchase totals = $942.91       $1,012.9225   $1,012.92   $1,013.00   $1,012.80