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	$190.66	13.760%	$216.8948	$216.89	$216.90	$216.90
Purchase #2	$90.86	5.226%	$95.6083	$95.61	$95.60	$95.60
Purchase #3	$181.43	8.543%	$196.9296	$196.93	$196.95	$196.90
Purchase #4	$83.58	13.412%	$94.7897	$94.79	$94.80	$94.80
Purchase #5	$96.63	10.481%	$106.7578	$106.76	$106.75	$106.80
Purchase #6	$160.58	6.223%	$170.5729	$170.57	$170.55	$170.60
Purchase #7	$71.41	9.180%	$77.9654	$77.97	$77.95	$78.00
7 purchase totals =	$875.15		$959.5185	$959.52	$959.50	$959.60