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 $84.98   11.461%   $94.7196   $94.72   $94.70   $94.70  
  Purchase #2 $24.95   7.613%   $26.8494   $26.85   $26.85   $26.80  
  Purchase #3 $62.65   5.176%   $65.8928   $65.89   $65.90   $65.90  
  Purchase #4 $76.30   10.506%   $84.3161   $84.32   $84.30   $84.30  
  Purchase #5 $117.29   8.290%   $127.0133   $127.01   $127.00   $127.00  
  Purchase #6 $89.27   12.757%   $100.6582   $100.66   $100.65   $100.70  
  Purchase #7 $229.58   13.794%   $261.2483   $261.25   $261.25   $261.20  
  7 purchase totals = $685.02       $760.6977   $760.70   $760.65   $760.60