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 $41.54   10.361%   $45.844   $45.84   $45.85   $45.80  
  Purchase #2 $85.46   9.358%   $93.4573   $93.46   $93.45   $93.50  
  Purchase #3 $69.41   12.695%   $78.2216   $78.22   $78.20   $78.20  
  Purchase #4 $240.98   5.389%   $253.9664   $253.97   $253.95   $254.00  
  Purchase #5 $171.70   3.568%   $177.8263   $177.83   $177.85   $177.80  
  Purchase #6 $184.66   5.429%   $194.6852   $194.69   $194.70   $194.70  
  Purchase #7 $47.47   10.394%   $52.404   $52.40   $52.40   $52.40  
  7 purchase totals = $841.22       $896.4048   $896.41   $896.40   $896.40