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 $250.47   12.551%   $281.9065   $281.91   $281.90   $281.90  
  Purchase #2 $57.65   10.665%   $63.7984   $63.80   $63.80   $63.80  
  Purchase #3 $43.27   13.319%   $49.0331   $49.03   $49.05   $49.00  
  Purchase #4 $44.43   10.667%   $49.1693   $49.17   $49.15   $49.20  
  Purchase #5 $194.85   3.273%   $201.2274   $201.23   $201.25   $201.20  
  Purchase #6 $201.57   11.428%   $224.6054   $224.61   $224.60   $224.60  
  Purchase #7 $69.98   3.132%   $72.1718   $72.17   $72.15   $72.20  
  7 purchase totals = $862.22       $941.9119   $941.92   $941.90   $941.90