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	$52.79	13.251%	$59.7852	$59.79	$59.80	$59.80
Purchase #2	$31.85	5.751%	$33.6817	$33.68	$33.70	$33.70
Purchase #3	$84.81	5.791%	$89.7213	$89.72	$89.70	$89.70
Purchase #4	$185.95	12.414%	$209.0338	$209.03	$209.05	$209.00
Purchase #5	$184.81	5.825%	$195.5752	$195.58	$195.60	$195.60
Purchase #6	$204.33	4.328%	$213.1734	$213.17	$213.15	$213.20
Purchase #7	$80.92	12.220%	$90.8084	$90.81	$90.80	$90.80
7 purchase totals =	$825.46		$891.7790	$891.78	$891.80	$891.80