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 $70.55   7.713%   $75.9915   $75.99   $76.00   $76.00  
  Purchase #2 $23.98   5.860%   $25.3852   $25.39   $25.40   $25.40  
  Purchase #3 $97.25   6.119%   $103.2007   $103.20   $103.20   $103.20  
  Purchase #4 $45.41   6.459%   $48.343   $48.34   $48.35   $48.30  
  Purchase #5 $194.77   7.671%   $209.7108   $209.71   $209.70   $209.70  
  Purchase #6 $90.65   3.338%   $93.6759   $93.68   $93.70   $93.70  
  Purchase #7 $129.98   5.857%   $137.5929   $137.59   $137.60   $137.60  
  7 purchase totals = $652.59       $693.9000   $693.90   $693.95   $693.90