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	$48.90	3.331%	$50.5289	$50.53	$50.55	$50.50
Purchase #2	$35.43	6.565%	$37.756	$37.76	$37.75	$37.80
Purchase #3	$42.71	6.832%	$45.6279	$45.63	$45.65	$45.60
Purchase #4	$61.65	6.145%	$65.4384	$65.44	$65.45	$65.40
Purchase #5	$37.86	10.366%	$41.7846	$41.78	$41.80	$41.80
Purchase #6	$14.96	4.374%	$15.6144	$15.61	$15.60	$15.60
Purchase #7	$208.93	6.535%	$222.5836	$222.58	$222.60	$222.60
7 purchase totals =	$450.44		$479.3338	$479.33	$479.40	$479.30