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	$48.52	7.378%	$52.0998	$52.10	$52.10	$52.10
Purchase #2	$18.97	13.636%	$21.5567	$21.56	$21.55	$21.60
Purchase #3	$116.70	12.684%	$131.5022	$131.50	$131.50	$131.50
Purchase #4	$126.82	7.741%	$136.6371	$136.64	$136.65	$136.60
Purchase #5	$223.86	13.561%	$254.2177	$254.22	$254.20	$254.20
Purchase #6	$70.42	4.438%	$73.5452	$73.55	$73.55	$73.50
Purchase #7	$213.56	4.689%	$223.5738	$223.57	$223.55	$223.60
7 purchase totals =	$818.85		$893.1325	$893.14	$893.10	$893.10