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	$29.80	5.411%	$31.4125	$31.41	$31.40	$31.40
Purchase #2	$16.62	6.124%	$17.6378	$17.64	$17.65	$17.60
Purchase #3	$62.73	4.508%	$65.5579	$65.56	$65.55	$65.60
Purchase #4	$130.71	12.130%	$146.5651	$146.57	$146.55	$146.60
Purchase #5	$52.50	13.744%	$59.7156	$59.72	$59.70	$59.70
Purchase #6	$49.90	10.500%	$55.1395	$55.14	$55.15	$55.10
Purchase #7	$79.83	7.184%	$85.565	$85.57	$85.55	$85.60
7 purchase totals =	$422.09		$461.5934	$461.61	$461.55	$461.60