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	$136.79	10.452%	$151.0873	$151.09	$151.10	$151.10
Purchase #2	$206.78	8.263%	$223.8662	$223.87	$223.85	$223.90
Purchase #3	$175.76	11.604%	$196.1552	$196.16	$196.15	$196.20
Purchase #4	$70.56	11.461%	$78.6469	$78.65	$78.65	$78.60
Purchase #5	$9.67	11.115%	$10.7448	$10.74	$10.75	$10.70
Purchase #6	$89.97	4.378%	$93.9089	$93.91	$93.90	$93.90
Purchase #7	$26.35	12.775%	$29.7162	$29.72	$29.70	$29.70
7 purchase totals =	$715.88		$784.1255	$784.14	$784.10	$784.10