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 $42.63   10.345%   $47.0401   $47.04   $47.05   $47.00  
  Purchase #2 $217.35   6.662%   $231.8299   $231.83   $231.85   $231.80  
  Purchase #3 $138.71   7.716%   $149.4129   $149.41   $149.40   $149.40  
  Purchase #4 $249.88   12.477%   $281.0575   $281.06   $281.05   $281.10  
  Purchase #5 $149.85   6.214%   $159.1617   $159.16   $159.15   $159.20  
  Purchase #6 $235.25   10.615%   $260.2218   $260.22   $260.20   $260.20  
  Purchase #7 $103.32   8.705%   $112.314   $112.31   $112.30   $112.30  
  7 purchase totals = $1,136.99       $1,241.0379   $1,241.03   $1,241.00   $1,241.00