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 $78.74   8.781%   $85.6542   $85.65   $85.65   $85.70  
  Purchase #2 $42.73   8.437%   $46.3351   $46.34   $46.35   $46.30  
  Purchase #3 $196.44   5.266%   $206.7845   $206.78   $206.80   $206.80  
  Purchase #4 $238.62   9.246%   $260.6828   $260.68   $260.70   $260.70  
  Purchase #5 $222.28   10.690%   $246.0417   $246.04   $246.05   $246.00  
  Purchase #6 $126.63   6.641%   $135.0395   $135.04   $135.05   $135.00  
  Purchase #7 $33.25   9.124%   $36.2837   $36.28   $36.30   $36.30  
  7 purchase totals = $938.69       $1,016.8215   $1,016.81   $1,016.90   $1,016.80