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 $61.84   11.268%   $68.8081   $68.81   $68.80   $68.80  
  Purchase #2 $14.93   9.677%   $16.3748   $16.37   $16.35   $16.40  
  Purchase #3 $245.81   10.791%   $272.3354   $272.34   $272.35   $272.30  
  Purchase #4 $40.88   3.507%   $42.3137   $42.31   $42.30   $42.30  
  Purchase #5 $247.89   5.470%   $261.4496   $261.45   $261.45   $261.40  
  Purchase #6 $215.81   5.722%   $228.1586   $228.16   $228.15   $228.20  
  Purchase #7 $119.91   13.518%   $136.1194   $136.12   $136.10   $136.10  
  7 purchase totals = $947.07       $1,025.5596   $1,025.56   $1,025.50   $1,025.50