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	$84.65	5.285%	$89.1238	$89.12	$89.10	$89.10
Purchase #2	$191.94	7.238%	$205.8326	$205.83	$205.85	$205.80
Purchase #3	$152.95	11.353%	$170.3144	$170.31	$170.30	$170.30
Purchase #4	$174.94	13.592%	$198.7178	$198.72	$198.70	$198.70
Purchase #5	$29.93	8.610%	$32.507	$32.51	$32.50	$32.50
Purchase #6	$78.98	6.712%	$84.2811	$84.28	$84.30	$84.30
Purchase #7	$239.80	11.123%	$266.473	$266.47	$266.45	$266.50
7 purchase totals =	$953.19		$1,047.2497	$1,047.24	$1,047.20	$1,047.20