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 $243.83   7.454%   $262.0051   $262.01   $262.00   $262.00  
  Purchase #2 $88.81   9.613%   $97.3473   $97.35   $97.35   $97.30  
  Purchase #3 $225.78   6.290%   $239.9816   $239.98   $240.00   $240.00  
  Purchase #4 $101.53   4.235%   $105.8298   $105.83   $105.85   $105.80  
  Purchase #5 $129.79   4.165%   $135.1958   $135.20   $135.20   $135.20  
  Purchase #6 $81.87   13.475%   $92.902   $92.90   $92.90   $92.90  
  Purchase #7 $40.93   6.629%   $43.6432   $43.64   $43.65   $43.60  
  7 purchase totals = $912.54       $976.9048   $976.91   $976.95   $976.80