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	$80.46	10.595%	$88.9847	$88.98	$89.00	$89.00
Purchase #2	$56.40	3.657%	$58.4625	$58.46	$58.45	$58.50
Purchase #3	$180.41	13.343%	$204.4821	$204.48	$204.50	$204.50
Purchase #4	$143.31	9.222%	$156.526	$156.53	$156.55	$156.50
Purchase #5	$47.48	8.358%	$51.4484	$51.45	$51.45	$51.40
Purchase #6	$19.35	13.518%	$21.9657	$21.97	$21.95	$22.00
Purchase #7	$94.97	10.180%	$104.6379	$104.64	$104.65	$104.60
7 purchase totals =	$622.38		$686.5073	$686.51	$686.55	$686.50