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 $32.34   8.845%   $35.2005   $35.20   $35.20   $35.20  
  Purchase #2 $166.78   5.343%   $175.6911   $175.69   $175.70   $175.70  
  Purchase #3 $68.56   11.656%   $76.5514   $76.55   $76.55   $76.60  
  Purchase #4 $125.89   4.470%   $131.5173   $131.52   $131.50   $131.50  
  Purchase #5 $204.97   13.671%   $232.9914   $232.99   $233.00   $233.00  
  Purchase #6 $87.60   10.519%   $96.8146   $96.81   $96.80   $96.80  
  Purchase #7 $146.96   3.259%   $151.7494   $151.75   $151.75   $151.70  
  7 purchase totals = $833.10       $900.5157   $900.51   $900.50   $900.50