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	$48.55	5.172%	$51.061	$51.06	$51.05	$51.10
Purchase #2	$127.77	10.638%	$141.3622	$141.36	$141.35	$141.40
Purchase #3	$171.31	13.177%	$193.8835	$193.88	$193.90	$193.90
Purchase #4	$104.73	5.819%	$110.8242	$110.82	$110.80	$110.80
Purchase #5	$191.53	9.386%	$209.507	$209.51	$209.50	$209.50
Purchase #6	$104.63	6.664%	$111.6025	$111.60	$111.60	$111.60
Purchase #7	$123.94	5.443%	$130.6861	$130.69	$130.70	$130.70
7 purchase totals =	$872.46		$948.9265	$948.92	$948.90	$949.00