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	$172.56	3.795%	$179.1087	$179.11	$179.10	$179.10
Purchase #2	$91.89	11.811%	$102.7431	$102.74	$102.75	$102.70
Purchase #3	$190.60	5.429%	$200.9477	$200.95	$200.95	$200.90
Purchase #4	$98.65	11.353%	$109.8497	$109.85	$109.85	$109.80
Purchase #5	$15.50	10.410%	$17.1136	$17.11	$17.10	$17.10
Purchase #6	$131.88	8.658%	$143.2982	$143.30	$143.30	$143.30
Purchase #7	$71.90	10.411%	$79.3855	$79.39	$79.40	$79.40
7 purchase totals =	$772.98		$832.4465	$832.45	$832.45	$832.30