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 $84.62   13.122%   $95.7238   $95.72   $95.70   $95.70  
  Purchase #2 $111.69   4.172%   $116.3497   $116.35   $116.35   $116.30  
  Purchase #3 $77.98   8.733%   $84.79   $84.79   $84.80   $84.80  
  Purchase #4 $90.61   3.518%   $93.7977   $93.80   $93.80   $93.80  
  Purchase #5 $33.63   8.585%   $36.5171   $36.52   $36.50   $36.50  
  Purchase #6 $209.89   13.609%   $238.4539   $238.45   $238.45   $238.50  
  Purchase #7 $94.93   8.545%   $103.0418   $103.04   $103.05   $103.00  
  7 purchase totals = $703.35       $768.6740   $768.67   $768.65   $768.60