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	$53.90	5.471%	$56.8489	$56.85	$56.85	$56.80
Purchase #2	$42.93	7.275%	$46.0532	$46.05	$46.05	$46.10
Purchase #3	$79.37	9.496%	$86.907	$86.91	$86.90	$86.90
Purchase #4	$137.28	6.805%	$146.6219	$146.62	$146.60	$146.60
Purchase #5	$31.76	6.686%	$33.8835	$33.88	$33.90	$33.90
Purchase #6	$21.88	3.823%	$22.7165	$22.72	$22.70	$22.70
Purchase #7	$190.50	9.791%	$209.1519	$209.15	$209.15	$209.20
7 purchase totals =	$557.62		$602.1829	$602.18	$602.15	$602.20