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	$75.90	9.126%	$82.8266	$82.83	$82.85	$82.80
Purchase #2	$236.51	6.843%	$252.6944	$252.69	$252.70	$252.70
Purchase #3	$204.31	11.676%	$228.1652	$228.17	$228.15	$228.20
Purchase #4	$53.77	3.148%	$55.4627	$55.46	$55.45	$55.50
Purchase #5	$40.99	4.369%	$42.7809	$42.78	$42.80	$42.80
Purchase #6	$193.55	11.510%	$215.8276	$215.83	$215.85	$215.80
Purchase #7	$107.76	4.621%	$112.7396	$112.74	$112.75	$112.70
7 purchase totals =	$912.79		$990.4970	$990.50	$990.55	$990.50