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	$34.78	6.816%	$37.1506	$37.15	$37.15	$37.20
Purchase #2	$100.25	6.637%	$106.9036	$106.90	$106.90	$106.90
Purchase #3	$145.25	13.250%	$164.4956	$164.50	$164.50	$164.50
Purchase #4	$28.61	5.695%	$30.2393	$30.24	$30.25	$30.20
Purchase #5	$67.30	9.383%	$73.6148	$73.61	$73.60	$73.60
Purchase #6	$112.45	9.704%	$123.3621	$123.36	$123.35	$123.40
Purchase #7	$12.98	13.512%	$14.7339	$14.73	$14.75	$14.70
7 purchase totals =	$501.62		$550.4999	$550.49	$550.50	$550.50