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 $83.86   12.503%   $94.345   $94.35   $94.35   $94.30  
  Purchase #2 $64.62   10.453%   $71.3747   $71.37   $71.35   $71.40  
  Purchase #3 $98.53   12.395%   $110.7428   $110.74   $110.75   $110.70  
  Purchase #4 $196.88   10.830%   $218.2021   $218.20   $218.20   $218.20  
  Purchase #5 $174.83   11.541%   $195.0071   $195.01   $195.00   $195.00  
  Purchase #6 $82.82   5.680%   $87.5242   $87.52   $87.50   $87.50  
  Purchase #7 $143.46   9.193%   $156.6483   $156.65   $156.65   $156.60  
  7 purchase totals = $845.00       $933.8442   $933.84   $933.80   $933.70