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 $168.41   10.591%   $186.2463   $186.25   $186.25   $186.20  
  Purchase #2 $188.42   8.174%   $203.8215   $203.82   $203.80   $203.80  
  Purchase #3 $58.39   3.401%   $60.3758   $60.38   $60.40   $60.40  
  Purchase #4 $181.37   12.554%   $204.1392   $204.14   $204.15   $204.10  
  Purchase #5 $125.26   3.129%   $129.1794   $129.18   $129.20   $129.20  
  Purchase #6 $95.63   10.557%   $105.7257   $105.73   $105.75   $105.70  
  Purchase #7 $113.25   12.359%   $127.2466   $127.25   $127.25   $127.20  
  7 purchase totals = $930.73       $1,016.7345   $1,016.75   $1,016.80   $1,016.60