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 $244.59   6.712%   $261.0069   $261.01   $261.00   $261.00  
  Purchase #2 $225.36   8.516%   $244.5517   $244.55   $244.55   $244.60  
  Purchase #3 $18.61   13.103%   $21.0485   $21.05   $21.05   $21.00  
  Purchase #4 $176.61   12.537%   $198.7516   $198.75   $198.75   $198.80  
  Purchase #5 $89.96   13.446%   $102.056   $102.06   $102.05   $102.10  
  Purchase #6 $212.48   4.611%   $222.2775   $222.28   $222.30   $222.30  
  Purchase #7 $246.27   3.231%   $254.227   $254.23   $254.25   $254.20  
  7 purchase totals = $1,213.88       $1,303.9192   $1,303.93   $1,303.95   $1,304.00