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	$138.83	7.230%	$148.8674	$148.87	$148.85	$148.90
Purchase #2	$128.27	3.168%	$132.3336	$132.33	$132.35	$132.30
Purchase #3	$79.74	3.261%	$82.3403	$82.34	$82.35	$82.30
Purchase #4	$191.56	10.208%	$211.1144	$211.11	$211.10	$211.10
Purchase #5	$249.55	10.417%	$275.5456	$275.55	$275.55	$275.50
Purchase #6	$180.26	3.132%	$185.9057	$185.91	$185.90	$185.90
Purchase #7	$39.85	7.262%	$42.7439	$42.74	$42.75	$42.70
7 purchase totals =	$1,008.06		$1,078.8509	$1,078.85	$1,078.85	$1,078.70