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 $215.34   13.335%   $244.0556   $244.06   $244.05   $244.10  
  Purchase #2 $161.54   13.423%   $183.2235   $183.22   $183.20   $183.20  
  Purchase #3 $108.49   9.640%   $118.9484   $118.95   $118.95   $118.90  
  Purchase #4 $159.39   4.756%   $166.9706   $166.97   $166.95   $167.00  
  Purchase #5 $80.88   8.473%   $87.733   $87.73   $87.75   $87.70  
  Purchase #6 $177.77   8.235%   $192.4094   $192.41   $192.40   $192.40  
  Purchase #7 $30.74   10.589%   $33.9951   $34.00   $34.00   $34.00  
  7 purchase totals = $934.15       $1,027.3356   $1,027.34   $1,027.30   $1,027.30