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 $231.57   6.343%   $246.2585   $246.26   $246.25   $246.30  
  Purchase #2 $57.66   11.317%   $64.1854   $64.19   $64.20   $64.20  
  Purchase #3 $14.49   11.416%   $16.1442   $16.14   $16.15   $16.10  
  Purchase #4 $147.46   13.266%   $167.022   $167.02   $167.00   $167.00  
  Purchase #5 $176.41   6.855%   $188.5029   $188.50   $188.50   $188.50  
  Purchase #6 $161.38   7.448%   $173.3996   $173.40   $173.40   $173.40  
  Purchase #7 $202.72   11.388%   $225.8058   $225.81   $225.80   $225.80  
  7 purchase totals = $991.69       $1,081.3184   $1,081.32   $1,081.30   $1,081.30