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 $244.37   10.167%   $269.2151   $269.22   $269.20   $269.20  
  Purchase #2 $160.47   13.180%   $181.6199   $181.62   $181.60   $181.60  
  Purchase #3 $15.76   11.480%   $17.5692   $17.57   $17.55   $17.60  
  Purchase #4 $151.78   4.472%   $158.5676   $158.57   $158.55   $158.60  
  Purchase #5 $107.91   11.146%   $119.9376   $119.94   $119.95   $119.90  
  Purchase #6 $95.37   9.651%   $104.5742   $104.57   $104.55   $104.60  
  Purchase #7 $6.92   7.835%   $7.4622   $7.46   $7.45   $7.50  
  7 purchase totals = $782.58       $858.9458   $858.95   $858.85   $859.00