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 $167.47   10.714%   $185.4127   $185.41   $185.40   $185.40  
  Purchase #2 $224.99   3.790%   $233.5171   $233.52   $233.50   $233.50  
  Purchase #3 $187.34   5.233%   $197.1435   $197.14   $197.15   $197.10  
  Purchase #4 $16.46   10.512%   $18.1903   $18.19   $18.20   $18.20  
  Purchase #5 $93.30   13.205%   $105.6203   $105.62   $105.60   $105.60  
  Purchase #6 $141.83   13.396%   $160.8295   $160.83   $160.85   $160.80  
  Purchase #7 $51.55   4.673%   $53.9589   $53.96   $53.95   $54.00  
  7 purchase totals = $882.94       $954.6723   $954.67   $954.65   $954.60