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 $195.66   12.835%   $220.773   $220.77   $220.75   $220.80  
  Purchase #2 $18.50   10.604%   $20.4617   $20.46   $20.45   $20.50  
  Purchase #3 $113.41   10.866%   $125.7331   $125.73   $125.75   $125.70  
  Purchase #4 $211.83   10.260%   $233.5638   $233.56   $233.55   $233.60  
  Purchase #5 $108.44   12.404%   $121.8909   $121.89   $121.90   $121.90  
  Purchase #6 $164.44   11.191%   $182.8425   $182.84   $182.85   $182.80  
  Purchase #7 $81.65   13.311%   $92.5184   $92.52   $92.50   $92.50  
  7 purchase totals = $893.93       $997.7834   $997.77   $997.75   $997.80