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	$141.90	3.251%	$146.5132	$146.51	$146.50	$146.50
Purchase #2	$235.83	9.143%	$257.3919	$257.39	$257.40	$257.40
Purchase #3	$249.88	13.218%	$282.9091	$282.91	$282.90	$282.90
Purchase #4	$203.77	4.613%	$213.1699	$213.17	$213.15	$213.20
Purchase #5	$23.86	3.235%	$24.6319	$24.63	$24.65	$24.60
Purchase #6	$36.96	10.738%	$40.9288	$40.93	$40.95	$40.90
Purchase #7	$220.33	6.836%	$235.3918	$235.39	$235.40	$235.40
7 purchase totals =	$1,112.53		$1,200.9366	$1,200.93	$1,200.95	$1,200.90