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	$168.91	6.169%	$179.3301	$179.33	$179.35	$179.30
Purchase #2	$209.88	3.337%	$216.8837	$216.88	$216.90	$216.90
Purchase #3	$34.34	11.325%	$38.229	$38.23	$38.25	$38.20
Purchase #4	$45.82	5.118%	$48.1651	$48.17	$48.15	$48.20
Purchase #5	$147.81	11.681%	$165.0757	$165.08	$165.10	$165.10
Purchase #6	$45.37	4.335%	$47.3368	$47.34	$47.35	$47.30
Purchase #7	$35.38	11.856%	$39.5747	$39.57	$39.55	$39.60
7 purchase totals =	$687.51		$734.5951	$734.60	$734.65	$734.60