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	$81.43	5.432%	$85.8533	$85.85	$85.85	$85.90
Purchase #2	$97.27	11.590%	$108.5436	$108.54	$108.55	$108.50
Purchase #3	$217.25	7.496%	$233.5351	$233.54	$233.55	$233.50
Purchase #4	$98.37	9.541%	$107.7555	$107.76	$107.75	$107.80
Purchase #5	$64.66	12.170%	$72.5291	$72.53	$72.55	$72.50
Purchase #6	$51.95	3.402%	$53.7173	$53.72	$53.70	$53.70
Purchase #7	$139.79	7.657%	$150.4937	$150.49	$150.50	$150.50
7 purchase totals =	$750.72		$812.4276	$812.43	$812.45	$812.40