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	$52.73	12.682%	$59.4172	$59.42	$59.40	$59.40
Purchase #2	$145.37	9.512%	$159.1976	$159.20	$159.20	$159.20
Purchase #3	$241.46	9.832%	$265.2003	$265.20	$265.20	$265.20
Purchase #4	$244.81	12.113%	$274.4638	$274.46	$274.45	$274.50
Purchase #5	$32.26	3.511%	$33.3926	$33.39	$33.40	$33.40
Purchase #6	$171.46	11.726%	$191.5654	$191.57	$191.55	$191.60
Purchase #7	$50.36	3.761%	$52.254	$52.25	$52.25	$52.30
7 purchase totals =	$938.45		$1,035.4909	$1,035.49	$1,035.45	$1,035.60