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	$88.74	13.674%	$100.8743	$100.87	$100.85	$100.90
Purchase #2	$40.31	13.729%	$45.8442	$45.84	$45.85	$45.80
Purchase #3	$169.65	6.319%	$180.3702	$180.37	$180.35	$180.40
Purchase #4	$223.42	8.437%	$242.2699	$242.27	$242.25	$242.30
Purchase #5	$132.73	10.861%	$147.1458	$147.15	$147.15	$147.10
Purchase #6	$112.34	4.620%	$117.5301	$117.53	$117.55	$117.50
Purchase #7	$167.48	4.711%	$175.37	$175.37	$175.35	$175.40
7 purchase totals =	$934.67		$1,009.4045	$1,009.40	$1,009.35	$1,009.40