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 $24.77   4.231%   $25.818   $25.82   $25.80   $25.80  
  Purchase #2 $63.39   9.817%   $69.613   $69.61   $69.60   $69.60  
  Purchase #3 $173.78   12.394%   $195.3183   $195.32   $195.30   $195.30  
  Purchase #4 $242.95   13.309%   $275.2842   $275.28   $275.30   $275.30  
  Purchase #5 $178.27   5.260%   $187.647   $187.65   $187.65   $187.60  
  Purchase #6 $23.26   4.173%   $24.2306   $24.23   $24.25   $24.20  
  Purchase #7 $171.91   13.114%   $194.4543   $194.45   $194.45   $194.50  
  7 purchase totals = $878.33       $972.3654   $972.36   $972.35   $972.30