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 $249.28   7.632%   $268.305   $268.31   $268.30   $268.30  
  Purchase #2 $180.72   7.781%   $194.7818   $194.78   $194.80   $194.80  
  Purchase #3 $65.82   3.598%   $68.1882   $68.19   $68.20   $68.20  
  Purchase #4 $118.40   4.436%   $123.6522   $123.65   $123.65   $123.70  
  Purchase #5 $142.66   7.627%   $153.5407   $153.54   $153.55   $153.50  
  Purchase #6 $126.85   7.727%   $136.6517   $136.65   $136.65   $136.70  
  Purchase #7 $16.96   12.363%   $19.0568   $19.06   $19.05   $19.10  
  7 purchase totals = $900.69       $964.1764   $964.18   $964.20   $964.30