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	$83.31	9.637%	$91.3386	$91.34	$91.35	$91.30
Purchase #2	$234.33	4.444%	$244.7436	$244.74	$244.75	$244.70
Purchase #3	$112.67	13.190%	$127.5312	$127.53	$127.55	$127.50
Purchase #4	$196.89	13.855%	$224.1691	$224.17	$224.15	$224.20
Purchase #5	$53.30	4.737%	$55.8248	$55.82	$55.80	$55.80
Purchase #6	$18.45	12.855%	$20.8217	$20.82	$20.80	$20.80
Purchase #7	$66.37	6.507%	$70.6887	$70.69	$70.70	$70.70
7 purchase totals =	$765.32		$835.1177	$835.11	$835.10	$835.00