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	$41.89	13.819%	$47.6788	$47.68	$47.70	$47.70
Purchase #2	$42.96	6.455%	$45.7331	$45.73	$45.75	$45.70
Purchase #3	$250.81	8.188%	$271.3463	$271.35	$271.35	$271.30
Purchase #4	$96.67	3.871%	$100.4121	$100.41	$100.40	$100.40
Purchase #5	$139.37	5.288%	$146.7399	$146.74	$146.75	$146.70
Purchase #6	$159.76	6.285%	$169.8009	$169.80	$169.80	$169.80
Purchase #7	$59.48	11.196%	$66.1394	$66.14	$66.15	$66.10
7 purchase totals =	$790.94		$847.8505	$847.85	$847.90	$847.70