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	$151.27	5.323%	$159.3221	$159.32	$159.30	$159.30
Purchase #2	$56.67	7.846%	$61.1163	$61.12	$61.10	$61.10
Purchase #3	$28.73	11.124%	$31.9259	$31.93	$31.95	$31.90
Purchase #4	$25.82	10.335%	$28.4885	$28.49	$28.50	$28.50
Purchase #5	$148.80	11.489%	$165.8956	$165.90	$165.90	$165.90
Purchase #6	$157.30	9.861%	$172.8114	$172.81	$172.80	$172.80
Purchase #7	$130.68	7.357%	$140.2941	$140.29	$140.30	$140.30
7 purchase totals =	$699.27		$759.8539	$759.86	$759.85	$759.80