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	$37.84	12.663%	$42.6317	$42.63	$42.65	$42.60
Purchase #2	$91.98	4.226%	$95.8671	$95.87	$95.85	$95.90
Purchase #3	$119.79	9.429%	$131.085	$131.09	$131.10	$131.10
Purchase #4	$219.95	11.303%	$244.8109	$244.81	$244.80	$244.80
Purchase #5	$120.60	11.372%	$134.3146	$134.31	$134.30	$134.30
Purchase #6	$168.73	4.202%	$175.82	$175.82	$175.80	$175.80
Purchase #7	$101.99	12.130%	$114.3614	$114.36	$114.35	$114.40
7 purchase totals =	$860.88		$938.8907	$938.89	$938.85	$938.90