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	$35.45	10.870%	$39.3034	$39.30	$39.30	$39.30
Purchase #2	$69.76	7.606%	$75.0659	$75.07	$75.05	$75.10
Purchase #3	$205.90	9.653%	$225.7755	$225.78	$225.80	$225.80
Purchase #4	$118.88	3.782%	$123.376	$123.38	$123.40	$123.40
Purchase #5	$38.96	6.455%	$41.4749	$41.47	$41.45	$41.50
Purchase #6	$172.40	6.442%	$183.506	$183.51	$183.50	$183.50
Purchase #7	$55.98	6.646%	$59.7004	$59.70	$59.70	$59.70
7 purchase totals =	$697.33		$748.2021	$748.21	$748.20	$748.30