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	$74.90	13.796%	$85.2332	$85.23	$85.25	$85.20
Purchase #2	$64.50	4.679%	$67.518	$67.52	$67.50	$67.50
Purchase #3	$84.87	6.416%	$90.3153	$90.32	$90.30	$90.30
Purchase #4	$45.63	13.283%	$51.691	$51.69	$51.70	$51.70
Purchase #5	$69.67	12.490%	$78.3718	$78.37	$78.35	$78.40
Purchase #6	$71.77	11.171%	$79.7874	$79.79	$79.80	$79.80
Purchase #7	$177.32	8.146%	$191.7645	$191.76	$191.75	$191.80
7 purchase totals =	$588.66		$644.6812	$644.68	$644.65	$644.70