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	$36.33	4.310%	$37.8958	$37.90	$37.90	$37.90
Purchase #2	$96.82	9.293%	$105.8175	$105.82	$105.80	$105.80
Purchase #3	$47.47	6.113%	$50.3718	$50.37	$50.35	$50.40
Purchase #4	$142.70	7.580%	$153.5167	$153.52	$153.50	$153.50
Purchase #5	$17.41	8.872%	$18.9546	$18.95	$18.95	$19.00
Purchase #6	$165.67	4.635%	$173.3488	$173.35	$173.35	$173.30
Purchase #7	$204.76	13.738%	$232.8899	$232.89	$232.90	$232.90
7 purchase totals =	$711.16		$772.7951	$772.80	$772.75	$772.80