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	$102.29	10.349%	$112.876	$112.88	$112.90	$112.90
Purchase #2	$139.50	4.708%	$146.0677	$146.07	$146.05	$146.10
Purchase #3	$10.55	7.343%	$11.3247	$11.32	$11.30	$11.30
Purchase #4	$73.85	13.608%	$83.8995	$83.90	$83.90	$83.90
Purchase #5	$122.87	5.378%	$129.4779	$129.48	$129.50	$129.50
Purchase #6	$42.96	5.197%	$45.1926	$45.19	$45.20	$45.20
Purchase #7	$82.73	9.301%	$90.4247	$90.42	$90.40	$90.40
7 purchase totals =	$574.75		$619.2631	$619.26	$619.25	$619.30