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 $53.52   13.517%   $60.7543   $60.75   $60.75   $60.80  
  Purchase #2 $248.34   12.509%   $279.4049   $279.40   $279.40   $279.40  
  Purchase #3 $109.78   3.867%   $114.0252   $114.03   $114.05   $114.00  
  Purchase #4 $78.75   13.221%   $89.1615   $89.16   $89.15   $89.20  
  Purchase #5 $93.25   13.843%   $106.1586   $106.16   $106.15   $106.20  
  Purchase #6 $138.42   3.562%   $143.3505   $143.35   $143.35   $143.40  
  Purchase #7 $242.67   6.305%   $257.9703   $257.97   $257.95   $258.00  
  7 purchase totals = $964.73       $1,050.8253   $1,050.82   $1,050.80   $1,051.00