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	$167.44	12.739%	$188.7702	$188.77	$188.75	$188.80
Purchase #2	$93.42	7.821%	$100.7264	$100.73	$100.75	$100.70
Purchase #3	$27.51	7.492%	$29.571	$29.57	$29.55	$29.60
Purchase #4	$31.43	7.697%	$33.8492	$33.85	$33.85	$33.80
Purchase #5	$88.50	10.870%	$98.12	$98.12	$98.10	$98.10
Purchase #6	$138.35	7.136%	$148.2227	$148.22	$148.20	$148.20
Purchase #7	$34.81	12.869%	$39.2897	$39.29	$39.30	$39.30
7 purchase totals =	$581.46		$638.5492	$638.55	$638.50	$638.50