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	$193.43	13.830%	$220.1814	$220.18	$220.20	$220.20
Purchase #2	$22.72	5.245%	$23.9117	$23.91	$23.90	$23.90
Purchase #3	$159.30	13.310%	$180.5028	$180.50	$180.50	$180.50
Purchase #4	$39.89	6.168%	$42.3504	$42.35	$42.35	$42.40
Purchase #5	$52.95	12.488%	$59.5624	$59.56	$59.55	$59.60
Purchase #6	$55.46	4.764%	$58.1021	$58.10	$58.10	$58.10
Purchase #7	$95.61	4.652%	$100.0578	$100.06	$100.05	$100.10
7 purchase totals =	$619.36		$684.6686	$684.66	$684.65	$684.80