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 $84.66   11.235%   $94.1716   $94.17   $94.15   $94.20  
  Purchase #2 $250.89   4.294%   $261.6632   $261.66   $261.65   $261.70  
  Purchase #3 $241.66   6.129%   $256.4713   $256.47   $256.45   $256.50  
  Purchase #4 $226.55   8.791%   $246.466   $246.47   $246.45   $246.50  
  Purchase #5 $189.55   7.261%   $203.3132   $203.31   $203.30   $203.30  
  Purchase #6 $97.97   10.366%   $108.1256   $108.13   $108.15   $108.10  
  Purchase #7 $106.70   9.183%   $116.4983   $116.50   $116.50   $116.50  
  7 purchase totals = $1,197.98       $1,286.7092   $1,286.71   $1,286.65   $1,286.80