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	$109.41	12.761%	$123.3718	$123.37	$123.35	$123.40
Purchase #2	$81.90	9.590%	$89.7542	$89.75	$89.75	$89.80
Purchase #3	$31.30	4.148%	$32.5983	$32.60	$32.60	$32.60
Purchase #4	$45.76	10.691%	$50.6522	$50.65	$50.65	$50.70
Purchase #5	$107.96	6.739%	$115.2354	$115.24	$115.25	$115.20
Purchase #6	$243.25	11.672%	$271.6421	$271.64	$271.65	$271.60
Purchase #7	$65.63	13.844%	$74.7158	$74.72	$74.70	$74.70
7 purchase totals =	$685.21		$757.9698	$757.97	$757.95	$758.00