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	$242.29	3.523%	$250.8259	$250.83	$250.85	$250.80
Purchase #2	$146.91	3.428%	$151.9461	$151.95	$151.95	$151.90
Purchase #3	$238.67	13.817%	$271.647	$271.65	$271.65	$271.60
Purchase #4	$223.79	13.583%	$254.1874	$254.19	$254.20	$254.20
Purchase #5	$131.25	3.601%	$135.9763	$135.98	$136.00	$136.00
Purchase #6	$136.88	7.284%	$146.8503	$146.85	$146.85	$146.90
Purchase #7	$28.88	12.377%	$32.4545	$32.45	$32.45	$32.50
7 purchase totals =	$1,148.67		$1,243.8875	$1,243.90	$1,243.95	$1,243.90