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	$6.63	10.530%	$7.3281	$7.33	$7.35	$7.30
Purchase #2	$44.37	4.182%	$46.2256	$46.23	$46.25	$46.20
Purchase #3	$40.30	8.500%	$43.7255	$43.73	$43.75	$43.70
Purchase #4	$144.86	11.668%	$161.7623	$161.76	$161.75	$161.80
Purchase #5	$88.40	4.810%	$92.652	$92.65	$92.65	$92.70
Purchase #6	$31.89	12.539%	$35.8887	$35.89	$35.90	$35.90
Purchase #7	$36.27	8.141%	$39.2227	$39.22	$39.20	$39.20
7 purchase totals =	$392.72		$426.8049	$426.81	$426.85	$426.80