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 $61.86   10.239%   $68.1938   $68.19   $68.20   $68.20  
  Purchase #2 $117.32   6.512%   $124.9599   $124.96   $124.95   $125.00  
  Purchase #3 $190.78   8.375%   $206.7578   $206.76   $206.75   $206.80  
  Purchase #4 $63.62   12.299%   $71.4446   $71.44   $71.45   $71.40  
  Purchase #5 $211.64   5.399%   $223.0664   $223.07   $223.05   $223.10  
  Purchase #6 $129.41   11.655%   $144.4927   $144.49   $144.50   $144.50  
  Purchase #7 $49.58   3.666%   $51.3976   $51.40   $51.40   $51.40  
  7 purchase totals = $824.21       $890.3128   $890.31   $890.30   $890.40