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	$85.72	4.457%	$89.5405	$89.54	$89.55	$89.50
Purchase #2	$169.49	10.685%	$187.6	$187.60	$187.60	$187.60
Purchase #3	$152.70	9.736%	$167.5669	$167.57	$167.55	$167.60
Purchase #4	$196.44	13.780%	$223.5094	$223.51	$223.50	$223.50
Purchase #5	$22.74	11.551%	$25.3667	$25.37	$25.35	$25.40
Purchase #6	$162.84	13.333%	$184.5515	$184.55	$184.55	$184.60
Purchase #7	$26.97	7.772%	$29.0661	$29.07	$29.05	$29.10
7 purchase totals =	$816.90		$907.2011	$907.21	$907.15	$907.30