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	$97.71	6.222%	$103.7895	$103.79	$103.80	$103.80
Purchase #2	$149.72	7.467%	$160.8996	$160.90	$160.90	$160.90
Purchase #3	$165.83	13.673%	$188.5039	$188.50	$188.50	$188.50
Purchase #4	$161.95	11.838%	$181.1216	$181.12	$181.10	$181.10
Purchase #5	$63.67	13.524%	$72.2807	$72.28	$72.30	$72.30
Purchase #6	$192.94	5.558%	$203.6636	$203.66	$203.65	$203.70
Purchase #7	$207.94	10.474%	$229.7196	$229.72	$229.70	$229.70
7 purchase totals =	$1,039.76		$1,139.9785	$1,139.97	$1,139.95	$1,140.00