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 $196.49   5.295%   $206.8941   $206.89   $206.90   $206.90  
  Purchase #2 $50.65   9.122%   $55.2703   $55.27   $55.25   $55.30  
  Purchase #3 $225.42   9.169%   $246.0888   $246.09   $246.10   $246.10  
  Purchase #4 $56.73   9.600%   $62.1761   $62.18   $62.20   $62.20  
  Purchase #5 $41.83   11.778%   $46.7567   $46.76   $46.75   $46.80  
  Purchase #6 $238.40   3.252%   $246.1528   $246.15   $246.15   $246.20  
  Purchase #7 $131.89   4.516%   $137.8462   $137.85   $137.85   $137.80  
  7 purchase totals = $941.41       $1,001.1850   $1,001.19   $1,001.20   $1,001.30