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	$215.30	6.749%	$229.8306	$229.83	$229.85	$229.80
Purchase #2	$225.38	13.116%	$254.9408	$254.94	$254.95	$254.90
Purchase #3	$166.35	7.802%	$179.3286	$179.33	$179.35	$179.30
Purchase #4	$190.80	4.830%	$200.0156	$200.02	$200.00	$200.00
Purchase #5	$53.97	5.322%	$56.8423	$56.84	$56.85	$56.80
Purchase #6	$47.32	12.339%	$53.1588	$53.16	$53.15	$53.20
Purchase #7	$87.33	4.321%	$91.1035	$91.10	$91.10	$91.10
7 purchase totals =	$986.45		$1,065.2202	$1,065.22	$1,065.25	$1,065.10