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 $189.33   9.658%   $207.6155   $207.62   $207.60   $207.60  
  Purchase #2 $61.51   9.335%   $67.252   $67.25   $67.25   $67.30  
  Purchase #3 $49.62   4.311%   $51.7591   $51.76   $51.75   $51.80  
  Purchase #4 $44.46   5.343%   $46.8355   $46.84   $46.85   $46.80  
  Purchase #5 $235.61   12.832%   $265.8435   $265.84   $265.85   $265.80  
  Purchase #6 $231.87   11.689%   $258.9733   $258.97   $258.95   $259.00  
  Purchase #7 $142.93   12.764%   $161.1736   $161.17   $161.15   $161.20  
  7 purchase totals = $955.33       $1,059.4525   $1,059.45   $1,059.40   $1,059.50