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 $245.27   12.801%   $276.667   $276.67   $276.65   $276.70  
  Purchase #2 $104.46   7.669%   $112.471   $112.47   $112.45   $112.50  
  Purchase #3 $211.32   7.712%   $227.617   $227.62   $227.60   $227.60  
  Purchase #4 $209.64   11.559%   $233.8723   $233.87   $233.85   $233.90  
  Purchase #5 $175.80   13.699%   $199.8828   $199.88   $199.90   $199.90  
  Purchase #6 $165.50   7.537%   $177.9737   $177.97   $177.95   $178.00  
  Purchase #7 $174.57   12.318%   $196.0735   $196.07   $196.05   $196.10  
  7 purchase totals = $1,286.56       $1,424.5573   $1,424.55   $1,424.45   $1,424.70