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	$203.85	12.375%	$229.0764	$229.08	$229.10	$229.10
Purchase #2	$242.81	4.403%	$253.5009	$253.50	$253.50	$253.50
Purchase #3	$141.58	11.873%	$158.3898	$158.39	$158.40	$158.40
Purchase #4	$60.73	7.447%	$65.2526	$65.25	$65.25	$65.30
Purchase #5	$153.50	9.198%	$167.6189	$167.62	$167.60	$167.60
Purchase #6	$182.59	4.677%	$191.1297	$191.13	$191.15	$191.10
Purchase #7	$165.60	12.612%	$186.4855	$186.49	$186.50	$186.50
7 purchase totals =	$1,150.66		$1,251.4538	$1,251.46	$1,251.50	$1,251.50