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 $52.39   4.667%   $54.835   $54.84   $54.85   $54.80  
  Purchase #2 $77.64   7.601%   $83.5414   $83.54   $83.55   $83.50  
  Purchase #3 $201.37   13.186%   $227.9226   $227.92   $227.90   $227.90  
  Purchase #4 $250.40   11.274%   $278.6301   $278.63   $278.65   $278.60  
  Purchase #5 $248.42   7.718%   $267.5931   $267.59   $267.60   $267.60  
  Purchase #6 $219.43   10.770%   $243.0626   $243.06   $243.05   $243.10  
  Purchase #7 $47.34   8.455%   $51.3426   $51.34   $51.35   $51.30  
  7 purchase totals = $1,096.99       $1,206.9274   $1,206.92   $1,206.95   $1,206.80