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	$140.29	3.431%	$145.1033	$145.10	$145.10	$145.10
Purchase #2	$182.78	6.653%	$194.9404	$194.94	$194.95	$194.90
Purchase #3	$127.80	12.398%	$143.6446	$143.64	$143.65	$143.60
Purchase #4	$64.55	4.283%	$67.3147	$67.31	$67.30	$67.30
Purchase #5	$147.26	9.184%	$160.7844	$160.78	$160.80	$160.80
Purchase #6	$246.66	12.250%	$276.8759	$276.88	$276.90	$276.90
Purchase #7	$86.39	7.473%	$92.8459	$92.85	$92.85	$92.80
7 purchase totals =	$995.73		$1,081.5092	$1,081.50	$1,081.55	$1,081.40