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	$120.80	4.732%	$126.5163	$126.52	$126.50	$126.50
Purchase #2	$90.57	9.321%	$99.012	$99.01	$99.00	$99.00
Purchase #3	$170.47	8.361%	$184.723	$184.72	$184.70	$184.70
Purchase #4	$55.89	8.826%	$60.8229	$60.82	$60.80	$60.80
Purchase #5	$105.88	11.485%	$118.0403	$118.04	$118.05	$118.00
Purchase #6	$224.65	6.849%	$240.0363	$240.04	$240.05	$240.00
Purchase #7	$157.88	10.472%	$174.4132	$174.41	$174.40	$174.40
7 purchase totals =	$926.14		$1,003.5640	$1,003.56	$1,003.50	$1,003.40