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	$135.88	9.294%	$148.5087	$148.51	$148.50	$148.50
Purchase #2	$85.31	3.282%	$88.1099	$88.11	$88.10	$88.10
Purchase #3	$117.46	13.861%	$133.7411	$133.74	$133.75	$133.70
Purchase #4	$172.73	8.806%	$187.9406	$187.94	$187.95	$187.90
Purchase #5	$32.72	5.630%	$34.5621	$34.56	$34.55	$34.60
Purchase #6	$142.42	9.670%	$156.192	$156.19	$156.20	$156.20
Purchase #7	$223.73	13.696%	$254.3721	$254.37	$254.35	$254.40
7 purchase totals =	$910.25		$1,003.4265	$1,003.42	$1,003.40	$1,003.40