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	$182.30	12.240%	$204.6135	$204.61	$204.60	$204.60
Purchase #2	$39.28	3.744%	$40.7506	$40.75	$40.75	$40.80
Purchase #3	$194.49	11.460%	$216.7786	$216.78	$216.80	$216.80
Purchase #4	$77.70	7.497%	$83.5252	$83.53	$83.55	$83.50
Purchase #5	$79.73	3.140%	$82.2335	$82.23	$82.25	$82.20
Purchase #6	$245.32	4.788%	$257.0659	$257.07	$257.05	$257.10
Purchase #7	$136.56	12.154%	$153.1575	$153.16	$153.15	$153.20
7 purchase totals =	$955.38		$1,038.1248	$1,038.13	$1,038.15	$1,038.20