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 $223.37   13.601%   $253.7506   $253.75   $253.75   $253.80  
  Purchase #2 $248.88   13.549%   $282.6008   $282.60   $282.60   $282.60  
  Purchase #3 $173.84   11.707%   $194.1914   $194.19   $194.20   $194.20  
  Purchase #4 $8.29   3.338%   $8.5667   $8.57   $8.55   $8.60  
  Purchase #5 $96.66   9.497%   $105.8398   $105.84   $105.85   $105.80  
  Purchase #6 $184.41   12.733%   $207.8909   $207.89   $207.90   $207.90  
  Purchase #7 $62.89   11.604%   $70.1878   $70.19   $70.20   $70.20  
  7 purchase totals = $998.34       $1,123.0280   $1,123.03   $1,123.05   $1,123.10