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	$29.90	5.233%	$31.4647	$31.46	$31.45	$31.50
Purchase #2	$68.65	3.842%	$71.2875	$71.29	$71.30	$71.30
Purchase #3	$135.70	12.128%	$152.1577	$152.16	$152.15	$152.20
Purchase #4	$236.38	11.235%	$262.9373	$262.94	$262.95	$262.90
Purchase #5	$152.76	3.760%	$158.5038	$158.50	$158.50	$158.50
Purchase #6	$168.45	13.445%	$191.0981	$191.10	$191.10	$191.10
Purchase #7	$31.41	10.371%	$34.6675	$34.67	$34.65	$34.70
7 purchase totals =	$823.25		$902.1166	$902.12	$902.10	$902.20