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	$71.41	10.513%	$78.9173	$78.92	$78.90	$78.90
Purchase #2	$221.54	3.542%	$229.3869	$229.39	$229.40	$229.40
Purchase #3	$40.87	4.674%	$42.7803	$42.78	$42.80	$42.80
Purchase #4	$35.28	5.117%	$37.0853	$37.09	$37.10	$37.10
Purchase #5	$249.95	12.167%	$280.3614	$280.36	$280.35	$280.40
Purchase #6	$65.72	3.782%	$68.2055	$68.21	$68.20	$68.20
Purchase #7	$210.47	4.422%	$219.777	$219.78	$219.80	$219.80
7 purchase totals =	$895.24		$956.5137	$956.53	$956.55	$956.60