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	$90.29	11.738%	$100.8882	$100.89	$100.90	$100.90
Purchase #2	$73.77	3.351%	$76.242	$76.24	$76.25	$76.20
Purchase #3	$80.75	3.567%	$83.6304	$83.63	$83.65	$83.60
Purchase #4	$62.82	3.194%	$64.8265	$64.83	$64.85	$64.80
Purchase #5	$240.67	11.660%	$268.7321	$268.73	$268.75	$268.70
Purchase #6	$223.39	6.603%	$238.1404	$238.14	$238.15	$238.10
Purchase #7	$213.86	12.766%	$241.1614	$241.16	$241.15	$241.20
7 purchase totals =	$985.55		$1,073.6210	$1,073.62	$1,073.70	$1,073.50