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	$64.54	3.672%	$66.9099	$66.91	$66.90	$66.90
Purchase #2	$227.30	7.247%	$243.7724	$243.77	$243.75	$243.80
Purchase #3	$42.60	3.195%	$43.9611	$43.96	$43.95	$44.00
Purchase #4	$34.89	5.828%	$36.9234	$36.92	$36.90	$36.90
Purchase #5	$193.85	8.803%	$210.9146	$210.91	$210.90	$210.90
Purchase #6	$175.80	13.258%	$199.1076	$199.11	$199.10	$199.10
Purchase #7	$31.33	4.750%	$32.8182	$32.82	$32.80	$32.80
7 purchase totals =	$770.31		$834.4072	$834.40	$834.30	$834.40