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 $23.97   6.118%   $25.4365   $25.44   $25.45   $25.40  
  Purchase #2 $54.71   6.647%   $58.3466   $58.35   $58.35   $58.30  
  Purchase #3 $35.45   7.149%   $37.9843   $37.98   $38.00   $38.00  
  Purchase #4 $128.27   3.327%   $132.5375   $132.54   $132.55   $132.50  
  Purchase #5 $92.79   12.746%   $104.617   $104.62   $104.60   $104.60  
  Purchase #6 $196.66   9.166%   $214.6859   $214.69   $214.70   $214.70  
  Purchase #7 $135.85   10.700%   $150.386   $150.39   $150.40   $150.40  
  7 purchase totals = $667.70       $723.9938   $724.01   $724.05   $723.90