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 $132.66   10.327%   $146.3598   $146.36   $146.35   $146.40  
  Purchase #2 $108.43   8.301%   $117.4308   $117.43   $117.45   $117.40  
  Purchase #3 $35.26   5.449%   $37.1813   $37.18   $37.20   $37.20  
  Purchase #4 $95.30   9.499%   $104.3525   $104.35   $104.35   $104.40  
  Purchase #5 $247.28   9.209%   $270.052   $270.05   $270.05   $270.10  
  Purchase #6 $117.86   12.384%   $132.4558   $132.46   $132.45   $132.50  
  Purchase #7 $50.43   8.138%   $54.534   $54.53   $54.55   $54.50  
  7 purchase totals = $787.22       $862.3662   $862.36   $862.40   $862.50