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	$113.71	12.788%	$128.2512	$128.25	$128.25	$128.30
Purchase #2	$91.67	8.174%	$99.1631	$99.16	$99.15	$99.20
Purchase #3	$99.64	5.742%	$105.3613	$105.36	$105.35	$105.40
Purchase #4	$108.26	11.858%	$121.0975	$121.10	$121.10	$121.10
Purchase #5	$123.61	8.654%	$134.3072	$134.31	$134.30	$134.30
Purchase #6	$68.52	3.802%	$71.1251	$71.13	$71.15	$71.10
Purchase #7	$151.34	12.496%	$170.2514	$170.25	$170.25	$170.30
7 purchase totals =	$756.75		$829.5568	$829.56	$829.55	$829.70