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 $222.87   11.128%   $247.671   $247.67   $247.65   $247.70  
  Purchase #2 $231.33   5.754%   $244.6407   $244.64   $244.65   $244.60  
  Purchase #3 $70.54   7.215%   $75.6295   $75.63   $75.65   $75.60  
  Purchase #4 $53.30   8.258%   $57.7015   $57.70   $57.70   $57.70  
  Purchase #5 $89.32   3.456%   $92.4069   $92.41   $92.40   $92.40  
  Purchase #6 $203.57   5.352%   $214.4651   $214.47   $214.45   $214.50  
  Purchase #7 $158.65   7.457%   $170.4805   $170.48   $170.50   $170.50  
  7 purchase totals = $1,029.58       $1,102.9952   $1,103.00   $1,103.00   $1,103.00