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 $31.76   6.252%   $33.7456   $33.75   $33.75   $33.70  
  Purchase #2 $173.78   13.680%   $197.5531   $197.55   $197.55   $197.60  
  Purchase #3 $112.44   4.718%   $117.7449   $117.74   $117.75   $117.70  
  Purchase #4 $10.80   5.542%   $11.3985   $11.40   $11.40   $11.40  
  Purchase #5 $214.89   9.268%   $234.806   $234.81   $234.80   $234.80  
  Purchase #6 $219.81   3.738%   $228.0265   $228.03   $228.05   $228.00  
  Purchase #7 $99.32   10.599%   $109.8469   $109.85   $109.85   $109.80  
  7 purchase totals = $862.80       $933.1215   $933.13   $933.15   $933.00