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	$158.58	4.366%	$165.5036	$165.50	$165.50	$165.50
Purchase #2	$78.75	13.337%	$89.2529	$89.25	$89.25	$89.30
Purchase #3	$151.28	7.846%	$163.1494	$163.15	$163.15	$163.10
Purchase #4	$72.72	11.241%	$80.8945	$80.89	$80.90	$80.90
Purchase #5	$194.73	10.843%	$215.8446	$215.84	$215.85	$215.80
Purchase #6	$220.90	13.524%	$250.7745	$250.77	$250.75	$250.80
Purchase #7	$243.68	13.737%	$277.1543	$277.15	$277.15	$277.20
7 purchase totals =	$1,120.64		$1,242.5738	$1,242.55	$1,242.55	$1,242.60