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 $224.81   13.607%   $255.3999   $255.40   $255.40   $255.40  
  Purchase #2 $112.65   12.409%   $126.6287   $126.63   $126.65   $126.60  
  Purchase #3 $11.61   5.687%   $12.2703   $12.27   $12.25   $12.30  
  Purchase #4 $168.29   9.719%   $184.6461   $184.65   $184.65   $184.60  
  Purchase #5 $229.57   5.735%   $242.7358   $242.74   $242.75   $242.70  
  Purchase #6 $45.84   4.601%   $47.9491   $47.95   $47.95   $47.90  
  Purchase #7 $178.55   8.639%   $193.9749   $193.97   $193.95   $194.00  
  7 purchase totals = $971.32       $1,063.6048   $1,063.61   $1,063.60   $1,063.50