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 $53.53   7.258%   $57.4152   $57.42   $57.40   $57.40  
  Purchase #2 $60.85   4.236%   $63.4276   $63.43   $63.45   $63.40  
  Purchase #3 $77.38   3.242%   $79.8887   $79.89   $79.90   $79.90  
  Purchase #4 $82.93   3.734%   $86.0266   $86.03   $86.05   $86.00  
  Purchase #5 $171.71   6.106%   $182.1946   $182.19   $182.20   $182.20  
  Purchase #6 $55.34   9.103%   $60.3776   $60.38   $60.40   $60.40  
  Purchase #7 $204.32   8.357%   $221.395   $221.40   $221.40   $221.40  
  7 purchase totals = $706.06       $750.7253   $750.74   $750.80   $750.70