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	$84.85	5.710%	$89.6949	$89.69	$89.70	$89.70
Purchase #2	$52.76	12.845%	$59.537	$59.54	$59.55	$59.50
Purchase #3	$209.61	7.619%	$225.5802	$225.58	$225.60	$225.60
Purchase #4	$6.89	13.603%	$7.8272	$7.83	$7.85	$7.80
Purchase #5	$108.56	4.707%	$113.6699	$113.67	$113.65	$113.70
Purchase #6	$216.97	10.669%	$240.1185	$240.12	$240.10	$240.10
Purchase #7	$165.28	13.343%	$187.3333	$187.33	$187.35	$187.30
7 purchase totals =	$844.92		$923.7610	$923.76	$923.80	$923.70