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 $223.89   10.721%   $247.8932   $247.89   $247.90   $247.90  
  Purchase #2 $186.51   12.406%   $209.6484   $209.65   $209.65   $209.60  
  Purchase #3 $191.75   6.471%   $204.1581   $204.16   $204.15   $204.20  
  Purchase #4 $161.90   12.181%   $181.621   $181.62   $181.60   $181.60  
  Purchase #5 $244.76   8.664%   $265.966   $265.97   $265.95   $266.00  
  Purchase #6 $218.57   6.589%   $232.9716   $232.97   $232.95   $233.00  
  Purchase #7 $221.50   10.569%   $244.9103   $244.91   $244.90   $244.90  
  7 purchase totals = $1,448.88       $1,587.1686   $1,587.17   $1,587.10   $1,587.20