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 $141.66   9.494%   $155.1092   $155.11   $155.10   $155.10  
  Purchase #2 $206.73   7.175%   $221.5629   $221.56   $221.55   $221.60  
  Purchase #3 $164.25   10.616%   $181.6868   $181.69   $181.70   $181.70  
  Purchase #4 $74.36   5.546%   $78.484   $78.48   $78.50   $78.50  
  Purchase #5 $14.82   4.110%   $15.4291   $15.43   $15.45   $15.40  
  Purchase #6 $245.86   3.635%   $254.797   $254.80   $254.80   $254.80  
  Purchase #7 $124.78   11.499%   $139.1285   $139.13   $139.15   $139.10  
  7 purchase totals = $972.46       $1,046.1975   $1,046.20   $1,046.25   $1,046.20