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	$74.59	13.215%	$84.4471	$84.45	$84.45	$84.40
Purchase #2	$242.73	9.472%	$265.7214	$265.72	$265.70	$265.70
Purchase #3	$109.34	6.546%	$116.4974	$116.50	$116.50	$116.50
Purchase #4	$78.67	5.417%	$82.9316	$82.93	$82.95	$82.90
Purchase #5	$11.74	13.528%	$13.3282	$13.33	$13.35	$13.30
Purchase #6	$109.50	9.175%	$119.5466	$119.55	$119.55	$119.50
Purchase #7	$180.32	4.684%	$188.7662	$188.77	$188.75	$188.80
7 purchase totals =	$806.89		$871.2385	$871.25	$871.25	$871.10