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 $46.33   9.591%   $50.7735   $50.77   $50.75   $50.80  
  Purchase #2 $218.33   5.572%   $230.4953   $230.50   $230.50   $230.50  
  Purchase #3 $207.67   5.408%   $218.9008   $218.90   $218.90   $218.90  
  Purchase #4 $93.58   4.203%   $97.5132   $97.51   $97.50   $97.50  
  Purchase #5 $236.74   3.260%   $244.4577   $244.46   $244.45   $244.50  
  Purchase #6 $214.56   4.662%   $224.5628   $224.56   $224.55   $224.60  
  Purchase #7 $147.90   7.158%   $158.4867   $158.49   $158.50   $158.50  
  7 purchase totals = $1,165.11       $1,225.1900   $1,225.19   $1,225.15   $1,225.30