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 $84.95   13.545%   $96.4565   $96.46   $96.45   $96.50  
  Purchase #2 $102.77   9.307%   $112.3348   $112.33   $112.35   $112.30  
  Purchase #3 $239.35   6.803%   $255.633   $255.63   $255.65   $255.60  
  Purchase #4 $86.35   6.180%   $91.6864   $91.69   $91.70   $91.70  
  Purchase #5 $139.28   4.516%   $145.5699   $145.57   $145.55   $145.60  
  Purchase #6 $7.55   5.383%   $7.9564   $7.96   $7.95   $8.00  
  Purchase #7 $112.73   6.439%   $119.9887   $119.99   $120.00   $120.00  
  7 purchase totals = $772.98       $829.6257   $829.63   $829.65   $829.70