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 $113.25   10.782%   $125.4606   $125.46   $125.45   $125.50  
  Purchase #2 $56.55   7.471%   $60.7749   $60.77   $60.75   $60.80  
  Purchase #3 $62.96   13.812%   $71.656   $71.66   $71.65   $71.70  
  Purchase #4 $141.44   7.791%   $152.4596   $152.46   $152.45   $152.50  
  Purchase #5 $191.92   11.139%   $213.298   $213.30   $213.30   $213.30  
  Purchase #6 $113.25   8.267%   $122.6124   $122.61   $122.60   $122.60  
  Purchase #7 $151.53   3.544%   $156.9002   $156.90   $156.90   $156.90  
  7 purchase totals = $830.90       $903.1617   $903.16   $903.10   $903.30