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	$49.86	11.302%	$55.4952	$55.50	$55.50	$55.50
Purchase #2	$139.72	13.354%	$158.3782	$158.38	$158.40	$158.40
Purchase #3	$68.52	7.599%	$73.7268	$73.73	$73.75	$73.70
Purchase #4	$96.29	5.324%	$101.4165	$101.42	$101.40	$101.40
Purchase #5	$123.51	13.258%	$139.885	$139.89	$139.90	$139.90
Purchase #6	$155.64	8.471%	$168.8243	$168.82	$168.80	$168.80
Purchase #7	$95.80	11.501%	$106.818	$106.82	$106.80	$106.80
7 purchase totals =	$729.34		$804.5440	$804.56	$804.55	$804.50