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	$53.73	13.443%	$60.9529	$60.95	$60.95	$61.00
Purchase #2	$74.56	11.566%	$83.1836	$83.18	$83.20	$83.20
Purchase #3	$72.88	10.146%	$80.2744	$80.27	$80.25	$80.30
Purchase #4	$145.77	5.807%	$154.2349	$154.23	$154.25	$154.20
Purchase #5	$42.87	11.450%	$47.7786	$47.78	$47.80	$47.80
Purchase #6	$32.35	10.560%	$35.7662	$35.77	$35.75	$35.80
Purchase #7	$53.74	5.299%	$56.5877	$56.59	$56.60	$56.60
7 purchase totals =	$475.90		$518.7783	$518.77	$518.80	$518.90