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 $177.64   11.437%   $197.9567   $197.96   $197.95   $198.00  
  Purchase #2 $161.54   8.822%   $175.7911   $175.79   $175.80   $175.80  
  Purchase #3 $126.60   6.395%   $134.6961   $134.70   $134.70   $134.70  
  Purchase #4 $227.71   5.850%   $241.031   $241.03   $241.05   $241.00  
  Purchase #5 $187.76   5.611%   $198.2952   $198.30   $198.30   $198.30  
  Purchase #6 $192.51   3.817%   $199.8581   $199.86   $199.85   $199.90  
  Purchase #7 $146.71   3.599%   $151.9901   $151.99   $152.00   $152.00  
  7 purchase totals = $1,220.47       $1,299.6183   $1,299.63   $1,299.65   $1,299.70