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	$241.52	13.226%	$273.4634	$273.46	$273.45	$273.50
Purchase #2	$110.52	4.403%	$115.3862	$115.39	$115.40	$115.40
Purchase #3	$188.49	11.515%	$210.1946	$210.19	$210.20	$210.20
Purchase #4	$237.70	11.847%	$265.8603	$265.86	$265.85	$265.90
Purchase #5	$196.88	9.517%	$215.6171	$215.62	$215.60	$215.60
Purchase #6	$70.42	11.440%	$78.476	$78.48	$78.50	$78.50
Purchase #7	$69.47	3.311%	$71.7702	$71.77	$71.75	$71.80
7 purchase totals =	$1,115.00		$1,230.7678	$1,230.77	$1,230.75	$1,230.90