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	$132.85	6.444%	$141.4109	$141.41	$141.40	$141.40
Purchase #2	$146.47	12.145%	$164.2588	$164.26	$164.25	$164.30
Purchase #3	$82.73	11.823%	$92.5112	$92.51	$92.50	$92.50
Purchase #4	$191.28	11.580%	$213.4302	$213.43	$213.45	$213.40
Purchase #5	$15.96	4.752%	$16.7184	$16.72	$16.70	$16.70
Purchase #6	$177.35	10.580%	$196.1136	$196.11	$196.10	$196.10
Purchase #7	$130.89	11.650%	$146.1387	$146.14	$146.15	$146.10
7 purchase totals =	$877.53		$970.5818	$970.58	$970.55	$970.50