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 $24.75   4.579%   $25.8833   $25.88   $25.90   $25.90  
  Purchase #2 $9.99   3.317%   $10.3214   $10.32   $10.30   $10.30  
  Purchase #3 $130.77   10.412%   $144.3858   $144.39   $144.40   $144.40  
  Purchase #4 $158.66   7.118%   $169.9534   $169.95   $169.95   $170.00  
  Purchase #5 $199.28   9.511%   $218.2335   $218.23   $218.25   $218.20  
  Purchase #6 $183.53   5.263%   $193.1892   $193.19   $193.20   $193.20  
  Purchase #7 $138.86   11.469%   $154.7859   $154.79   $154.80   $154.80  
  7 purchase totals = $845.84       $916.7525   $916.75   $916.80   $916.80