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	$148.74	5.492%	$156.9088	$156.91	$156.90	$156.90
Purchase #2	$228.35	6.477%	$243.1402	$243.14	$243.15	$243.10
Purchase #3	$197.95	10.307%	$218.3527	$218.35	$218.35	$218.40
Purchase #4	$153.34	4.289%	$159.9168	$159.92	$159.90	$159.90
Purchase #5	$156.48	10.262%	$172.538	$172.54	$172.55	$172.50
Purchase #6	$138.68	12.633%	$156.1994	$156.20	$156.20	$156.20
Purchase #7	$90.30	3.538%	$93.4948	$93.49	$93.50	$93.50
7 purchase totals =	$1,113.84		$1,200.5507	$1,200.55	$1,200.55	$1,200.50