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	$91.56	10.190%	$100.89	$100.89	$100.90	$100.90
Purchase #2	$106.61	11.687%	$119.0695	$119.07	$119.05	$119.10
Purchase #3	$158.87	6.218%	$168.7485	$168.75	$168.75	$168.70
Purchase #4	$105.89	9.257%	$115.6922	$115.69	$115.70	$115.70
Purchase #5	$193.34	6.370%	$205.6558	$205.66	$205.65	$205.70
Purchase #6	$50.59	13.230%	$57.2831	$57.28	$57.30	$57.30
Purchase #7	$155.71	6.210%	$165.3796	$165.38	$165.40	$165.40
7 purchase totals =	$862.57		$932.7187	$932.72	$932.75	$932.80