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	$149.85	12.661%	$168.8225	$168.82	$168.80	$168.80
Purchase #2	$235.92	5.258%	$248.3247	$248.32	$248.30	$248.30
Purchase #3	$37.87	6.537%	$40.3456	$40.35	$40.35	$40.30
Purchase #4	$202.32	10.537%	$223.6385	$223.64	$223.65	$223.60
Purchase #5	$158.48	5.692%	$167.5007	$167.50	$167.50	$167.50
Purchase #6	$81.77	4.639%	$85.5633	$85.56	$85.55	$85.60
Purchase #7	$46.91	8.859%	$51.0658	$51.07	$51.05	$51.10
7 purchase totals =	$913.12		$985.2611	$985.26	$985.20	$985.20