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	$234.68	8.837%	$255.4187	$255.42	$255.40	$255.40
Purchase #2	$86.89	13.446%	$98.5732	$98.57	$98.55	$98.60
Purchase #3	$244.96	4.636%	$256.3163	$256.32	$256.30	$256.30
Purchase #4	$170.43	8.478%	$184.8791	$184.88	$184.90	$184.90
Purchase #5	$93.56	5.607%	$98.8059	$98.81	$98.80	$98.80
Purchase #6	$38.79	10.517%	$42.8695	$42.87	$42.85	$42.90
Purchase #7	$78.94	6.136%	$83.7838	$83.78	$83.80	$83.80
7 purchase totals =	$948.25		$1,020.6465	$1,020.65	$1,020.60	$1,020.70