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	$123.52	6.798%	$131.9169	$131.92	$131.90	$131.90
Purchase #2	$38.92	3.142%	$40.1429	$40.14	$40.15	$40.10
Purchase #3	$205.71	7.170%	$220.4594	$220.46	$220.45	$220.50
Purchase #4	$97.67	12.702%	$110.076	$110.08	$110.10	$110.10
Purchase #5	$55.32	7.229%	$59.3191	$59.32	$59.30	$59.30
Purchase #6	$35.25	8.482%	$38.2399	$38.24	$38.25	$38.20
Purchase #7	$193.72	8.182%	$209.5702	$209.57	$209.55	$209.60
7 purchase totals =	$750.11		$809.7244	$809.73	$809.70	$809.70