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 $96.92   7.407%   $104.0989   $104.10   $104.10   $104.10  
  Purchase #2 $207.85   9.241%   $227.0574   $227.06   $227.05   $227.10  
  Purchase #3 $203.92   9.339%   $222.9641   $222.96   $222.95   $223.00  
  Purchase #4 $192.87   12.631%   $217.2314   $217.23   $217.25   $217.20  
  Purchase #5 $221.57   5.438%   $233.619   $233.62   $233.60   $233.60  
  Purchase #6 $234.78   11.324%   $261.3665   $261.37   $261.35   $261.40  
  Purchase #7 $153.49   8.703%   $166.8482   $166.85   $166.85   $166.80  
  7 purchase totals = $1,311.40       $1,433.1855   $1,433.19   $1,433.15   $1,433.20