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 $246.43   5.383%   $259.6953   $259.70   $259.70   $259.70  
  Purchase #2 $236.61   6.435%   $251.8359   $251.84   $251.85   $251.80  
  Purchase #3 $159.74   13.708%   $181.6372   $181.64   $181.65   $181.60  
  Purchase #4 $94.57   3.376%   $97.7627   $97.76   $97.75   $97.80  
  Purchase #5 $118.95   11.202%   $132.2748   $132.27   $132.25   $132.30  
  Purchase #6 $41.25   3.245%   $42.5886   $42.59   $42.60   $42.60  
  Purchase #7 $6.92   10.299%   $7.6327   $7.63   $7.65   $7.60  
  7 purchase totals = $904.47       $973.4272   $973.43   $973.45   $973.40