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 $192.49   5.254%   $202.6034   $202.60   $202.60   $202.60  
  Purchase #2 $49.92   10.482%   $55.1526   $55.15   $55.15   $55.20  
  Purchase #3 $13.33   12.465%   $14.9916   $14.99   $15.00   $15.00  
  Purchase #4 $175.72   4.255%   $183.1969   $183.20   $183.20   $183.20  
  Purchase #5 $148.76   3.453%   $153.8967   $153.90   $153.90   $153.90  
  Purchase #6 $111.86   11.214%   $124.404   $124.40   $124.40   $124.40  
  Purchase #7 $157.37   5.771%   $166.4518   $166.45   $166.45   $166.50  
  7 purchase totals = $849.45       $900.6970   $900.69   $900.70   $900.80