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 $118.83   6.413%   $126.4506   $126.45   $126.45   $126.50  
  Purchase #2 $65.25   5.467%   $68.8172   $68.82   $68.80   $68.80  
  Purchase #3 $23.42   13.118%   $26.4922   $26.49   $26.50   $26.50  
  Purchase #4 $100.52   10.152%   $110.7248   $110.72   $110.70   $110.70  
  Purchase #5 $90.49   12.863%   $102.1297   $102.13   $102.15   $102.10  
  Purchase #6 $33.57   11.494%   $37.4285   $37.43   $37.45   $37.40  
  Purchase #7 $116.89   6.489%   $124.475   $124.48   $124.50   $124.50  
  7 purchase totals = $548.97       $596.5180   $596.52   $596.55   $596.50