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 $164.51   13.140%   $186.1266   $186.13   $186.15   $186.10  
  Purchase #2 $116.35   9.724%   $127.6639   $127.66   $127.65   $127.70  
  Purchase #3 $224.92   9.265%   $245.7588   $245.76   $245.75   $245.80  
  Purchase #4 $221.85   8.110%   $239.842   $239.84   $239.85   $239.80  
  Purchase #5 $195.62   4.269%   $203.971   $203.97   $203.95   $204.00  
  Purchase #6 $218.54   8.410%   $236.9192   $236.92   $236.90   $236.90  
  Purchase #7 $23.97   8.429%   $25.9904   $25.99   $26.00   $26.00  
  7 purchase totals = $1,165.76       $1,266.2719   $1,266.27   $1,266.25   $1,266.30