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	$39.75	7.738%	$42.8259	$42.83	$42.85	$42.80
Purchase #2	$138.47	12.368%	$155.596	$155.60	$155.60	$155.60
Purchase #3	$69.29	8.406%	$75.1145	$75.11	$75.10	$75.10
Purchase #4	$217.48	10.693%	$240.7351	$240.74	$240.75	$240.70
Purchase #5	$98.91	10.499%	$109.2946	$109.29	$109.30	$109.30
Purchase #6	$90.28	11.763%	$100.8996	$100.90	$100.90	$100.90
Purchase #7	$205.36	5.214%	$216.0675	$216.07	$216.05	$216.10
7 purchase totals =	$859.54		$940.5332	$940.54	$940.55	$940.50