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	$169.96	12.234%	$190.7529	$190.75	$190.75	$190.80
Purchase #2	$73.34	9.779%	$80.5119	$80.51	$80.50	$80.50
Purchase #3	$142.45	8.757%	$154.9243	$154.92	$154.90	$154.90
Purchase #4	$175.74	11.278%	$195.56	$195.56	$195.55	$195.60
Purchase #5	$82.45	10.275%	$90.9217	$90.92	$90.90	$90.90
Purchase #6	$180.93	4.119%	$188.3825	$188.38	$188.40	$188.40
Purchase #7	$50.53	12.125%	$56.6568	$56.66	$56.65	$56.70
7 purchase totals =	$875.40		$957.7101	$957.70	$957.65	$957.80