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 $71.93   3.774%   $74.6446   $74.64   $74.65   $74.60  
  Purchase #2 $214.74   10.241%   $236.7315   $236.73   $236.75   $236.70  
  Purchase #3 $168.48   9.521%   $184.521   $184.52   $184.50   $184.50  
  Purchase #4 $180.39   9.483%   $197.4964   $197.50   $197.50   $197.50  
  Purchase #5 $106.48   7.197%   $114.1434   $114.14   $114.15   $114.10  
  Purchase #6 $58.93   8.463%   $63.9172   $63.92   $63.90   $63.90  
  Purchase #7 $101.46   10.355%   $111.9662   $111.97   $111.95   $112.00  
  7 purchase totals = $902.41       $983.4203   $983.42   $983.40   $983.30