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	$55.78	5.291%	$58.7313	$58.73	$58.75	$58.70
Purchase #2	$97.31	5.158%	$102.3292	$102.33	$102.35	$102.30
Purchase #3	$178.69	3.690%	$185.2837	$185.28	$185.30	$185.30
Purchase #4	$99.58	12.496%	$112.0235	$112.02	$112.00	$112.00
Purchase #5	$220.55	5.847%	$233.4456	$233.45	$233.45	$233.40
Purchase #6	$100.91	8.519%	$109.5065	$109.51	$109.50	$109.50
Purchase #7	$175.77	9.821%	$193.0324	$193.03	$193.05	$193.00
7 purchase totals =	$928.59		$994.3522	$994.35	$994.40	$994.20