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 $175.27   5.778%   $185.3971   $185.40   $185.40   $185.40  
  Purchase #2 $237.83   3.274%   $245.6166   $245.62   $245.60   $245.60  
  Purchase #3 $21.75   11.519%   $24.2554   $24.26   $24.25   $24.30  
  Purchase #4 $186.37   5.623%   $196.8496   $196.85   $196.85   $196.80  
  Purchase #5 $87.94   9.607%   $96.3884   $96.39   $96.40   $96.40  
  Purchase #6 $110.39   8.325%   $119.58   $119.58   $119.60   $119.60  
  Purchase #7 $221.37   7.464%   $237.8931   $237.89   $237.90   $237.90  
  7 purchase totals = $1,040.92       $1,105.9802   $1,105.99   $1,106.00   $1,106.00