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 $82.79   12.524%   $93.1586   $93.16   $93.15   $93.20  
  Purchase #2 $95.96   9.586%   $105.1587   $105.16   $105.15   $105.20  
  Purchase #3 $129.96   7.513%   $139.7239   $139.72   $139.70   $139.70  
  Purchase #4 $236.35   8.593%   $256.6596   $256.66   $256.65   $256.70  
  Purchase #5 $42.90   6.489%   $45.6838   $45.68   $45.70   $45.70  
  Purchase #6 $130.34   9.232%   $142.373   $142.37   $142.35   $142.40  
  Purchase #7 $60.90   5.462%   $64.2264   $64.23   $64.25   $64.20  
  7 purchase totals = $779.20       $846.9840   $846.98   $846.95   $847.10