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	$48.75	4.287%	$50.8399	$50.84	$50.85	$50.80
Purchase #2	$57.49	7.107%	$61.5758	$61.58	$61.60	$61.60
Purchase #3	$117.44	11.756%	$131.2462	$131.25	$131.25	$131.20
Purchase #4	$30.56	6.745%	$32.6213	$32.62	$32.60	$32.60
Purchase #5	$148.48	4.640%	$155.3695	$155.37	$155.35	$155.40
Purchase #6	$218.74	4.411%	$228.3886	$228.39	$228.40	$228.40
Purchase #7	$130.35	4.763%	$136.5586	$136.56	$136.55	$136.60
7 purchase totals =	$751.81		$796.5999	$796.61	$796.60	$796.60