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	$11.52	9.692%	$12.6365	$12.64	$12.65	$12.60
Purchase #2	$204.90	6.830%	$218.8947	$218.89	$218.90	$218.90
Purchase #3	$116.67	5.735%	$123.361	$123.36	$123.35	$123.40
Purchase #4	$99.65	3.680%	$103.3171	$103.32	$103.30	$103.30
Purchase #5	$175.49	4.827%	$183.9609	$183.96	$183.95	$184.00
Purchase #6	$120.99	12.679%	$136.3303	$136.33	$136.35	$136.30
Purchase #7	$205.43	8.787%	$223.4811	$223.48	$223.50	$223.50
7 purchase totals =	$934.65		$1,001.9816	$1,001.98	$1,002.00	$1,002.00