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	$68.30	6.180%	$72.5209	$72.52	$72.50	$72.50
Purchase #2	$141.68	11.426%	$157.8684	$157.87	$157.85	$157.90
Purchase #3	$150.53	9.285%	$164.5067	$164.51	$164.50	$164.50
Purchase #4	$165.75	12.123%	$185.8439	$185.84	$185.85	$185.80
Purchase #5	$197.31	6.104%	$209.3538	$209.35	$209.35	$209.40
Purchase #6	$25.33	11.181%	$28.1621	$28.16	$28.15	$28.20
Purchase #7	$79.82	4.205%	$83.1764	$83.18	$83.20	$83.20
7 purchase totals =	$828.72		$901.4322	$901.43	$901.40	$901.50