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 $73.83   13.801%   $84.0193   $84.02   $84.00   $84.00  
  Purchase #2 $108.99   13.712%   $123.9347   $123.93   $123.95   $123.90  
  Purchase #3 $122.85   3.109%   $126.6694   $126.67   $126.65   $126.70  
  Purchase #4 $238.79   9.597%   $261.7067   $261.71   $261.70   $261.70  
  Purchase #5 $136.96   8.641%   $148.7947   $148.79   $148.80   $148.80  
  Purchase #6 $116.35   13.827%   $132.4377   $132.44   $132.45   $132.40  
  Purchase #7 $124.79   5.267%   $131.3627   $131.36   $131.35   $131.40  
  7 purchase totals = $922.56       $1,008.9252   $1,008.92   $1,008.90   $1,008.90