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 $77.69   7.320%   $83.3769   $83.38   $83.40   $83.40  
  Purchase #2 $59.69   11.293%   $66.4308   $66.43   $66.45   $66.40  
  Purchase #3 $118.71   11.773%   $132.6857   $132.69   $132.70   $132.70  
  Purchase #4 $245.50   6.807%   $262.2112   $262.21   $262.20   $262.20  
  Purchase #5 $126.83   7.565%   $136.4247   $136.42   $136.40   $136.40  
  Purchase #6 $67.92   8.446%   $73.6565   $73.66   $73.65   $73.70  
  Purchase #7 $247.66   11.617%   $276.4307   $276.43   $276.45   $276.40  
  7 purchase totals = $944.00       $1,031.2165   $1,031.22   $1,031.25   $1,031.20