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	$34.53	5.479%	$36.4219	$36.42	$36.40	$36.40
Purchase #2	$192.37	12.767%	$216.9299	$216.93	$216.95	$216.90
Purchase #3	$83.74	7.708%	$90.1947	$90.19	$90.20	$90.20
Purchase #4	$186.35	4.559%	$194.8457	$194.85	$194.85	$194.80
Purchase #5	$130.83	12.598%	$147.312	$147.31	$147.30	$147.30
Purchase #6	$123.71	3.367%	$127.8753	$127.88	$127.90	$127.90
Purchase #7	$31.41	6.648%	$33.4981	$33.50	$33.50	$33.50
7 purchase totals =	$782.94		$847.0776	$847.08	$847.10	$847.00