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 $62.48   3.272%   $64.5243   $64.52   $64.50   $64.50  
  Purchase #2 $240.60   4.277%   $250.8905   $250.89   $250.90   $250.90  
  Purchase #3 $194.79   3.694%   $201.9855   $201.99   $202.00   $202.00  
  Purchase #4 $35.96   5.687%   $38.005   $38.01   $38.00   $38.00  
  Purchase #5 $153.56   3.756%   $159.3277   $159.33   $159.35   $159.30  
  Purchase #6 $70.44   11.135%   $78.2835   $78.28   $78.30   $78.30  
  Purchase #7 $151.58   13.424%   $171.9281   $171.93   $171.95   $171.90  
  7 purchase totals = $909.41       $964.9446   $964.95   $965.00   $964.90