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	$48.71	3.619%	$50.4728	$50.47	$50.45	$50.50
Purchase #2	$73.36	6.856%	$78.3896	$78.39	$78.40	$78.40
Purchase #3	$130.29	5.568%	$137.5445	$137.54	$137.55	$137.50
Purchase #4	$33.39	12.371%	$37.5207	$37.52	$37.50	$37.50
Purchase #5	$140.77	7.623%	$151.5009	$151.50	$151.50	$151.50
Purchase #6	$163.36	5.140%	$171.7567	$171.76	$171.75	$171.80
Purchase #7	$70.44	11.241%	$78.3582	$78.36	$78.35	$78.40
7 purchase totals =	$660.32		$705.5434	$705.54	$705.50	$705.60