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	$29.57	10.272%	$32.6074	$32.61	$32.60	$32.60
Purchase #2	$245.97	3.448%	$254.451	$254.45	$254.45	$254.50
Purchase #3	$26.29	8.296%	$28.471	$28.47	$28.45	$28.50
Purchase #4	$223.34	12.349%	$250.9203	$250.92	$250.90	$250.90
Purchase #5	$84.91	4.469%	$88.7046	$88.70	$88.70	$88.70
Purchase #6	$131.35	10.326%	$144.9132	$144.91	$144.90	$144.90
Purchase #7	$156.60	10.343%	$172.7971	$172.80	$172.80	$172.80
7 purchase totals =	$898.03		$972.8646	$972.86	$972.80	$972.90