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	$52.88	11.835%	$59.1383	$59.14	$59.15	$59.10
Purchase #2	$215.65	10.471%	$238.2307	$238.23	$238.25	$238.20
Purchase #3	$32.79	8.224%	$35.4866	$35.49	$35.50	$35.50
Purchase #4	$185.39	4.241%	$193.2524	$193.25	$193.25	$193.30
Purchase #5	$166.96	11.210%	$185.6762	$185.68	$185.70	$185.70
Purchase #6	$75.70	13.821%	$86.1625	$86.16	$86.15	$86.20
Purchase #7	$38.28	11.740%	$42.7741	$42.77	$42.75	$42.80
7 purchase totals =	$767.65		$840.7208	$840.72	$840.75	$840.80