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 $14.60   3.697%   $15.1398   $15.14   $15.15   $15.10  
  Purchase #2 $240.41   12.149%   $269.6174   $269.62   $269.60   $269.60  
  Purchase #3 $135.52   12.607%   $152.605   $152.61   $152.60   $152.60  
  Purchase #4 $197.70   13.108%   $223.6145   $223.61   $223.60   $223.60  
  Purchase #5 $43.49   8.297%   $47.0984   $47.10   $47.10   $47.10  
  Purchase #6 $157.71   8.190%   $170.6264   $170.63   $170.65   $170.60  
  Purchase #7 $42.38   9.355%   $46.3446   $46.34   $46.35   $46.30  
  7 purchase totals = $831.81       $925.0461   $925.05   $925.05   $924.90