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 $141.66   3.738%   $146.9553   $146.96   $146.95   $147.00  
  Purchase #2 $243.37   13.301%   $275.7406   $275.74   $275.75   $275.70  
  Purchase #3 $161.73   9.700%   $177.4178   $177.42   $177.40   $177.40  
  Purchase #4 $247.62   6.401%   $263.4702   $263.47   $263.45   $263.50  
  Purchase #5 $224.76   5.857%   $237.9242   $237.92   $237.90   $237.90  
  Purchase #6 $122.96   8.605%   $133.5407   $133.54   $133.55   $133.50  
  Purchase #7 $169.68   8.830%   $184.6627   $184.66   $184.65   $184.70  
  7 purchase totals = $1,311.78       $1,419.7115   $1,419.71   $1,419.65   $1,419.70