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	$79.40	12.629%	$89.4274	$89.43	$89.45	$89.40
Purchase #2	$193.72	12.235%	$217.4216	$217.42	$217.40	$217.40
Purchase #3	$112.46	11.434%	$125.3187	$125.32	$125.30	$125.30
Purchase #4	$128.67	9.518%	$140.9168	$140.92	$140.90	$140.90
Purchase #5	$74.27	11.761%	$83.0049	$83.00	$83.00	$83.00
Purchase #6	$216.39	8.308%	$234.3677	$234.37	$234.35	$234.40
Purchase #7	$37.51	7.524%	$40.3323	$40.33	$40.35	$40.30
7 purchase totals =	$842.42		$930.7894	$930.79	$930.75	$930.70