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	$135.79	8.165%	$146.8773	$146.88	$146.90	$146.90
Purchase #2	$140.65	12.642%	$158.431	$158.43	$158.45	$158.40
Purchase #3	$149.55	6.245%	$158.8894	$158.89	$158.90	$158.90
Purchase #4	$78.78	13.668%	$89.5477	$89.55	$89.55	$89.50
Purchase #5	$119.28	10.704%	$132.0477	$132.05	$132.05	$132.00
Purchase #6	$122.85	5.428%	$129.5183	$129.52	$129.50	$129.50
Purchase #7	$127.47	6.138%	$135.2941	$135.29	$135.30	$135.30
7 purchase totals =	$874.37		$950.6055	$950.61	$950.65	$950.50