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	$46.76	4.441%	$48.8366	$48.84	$48.85	$48.80
Purchase #2	$206.92	7.556%	$222.5549	$222.55	$222.55	$222.60
Purchase #3	$69.52	11.507%	$77.5197	$77.52	$77.50	$77.50
Purchase #4	$116.57	6.610%	$124.2753	$124.28	$124.30	$124.30
Purchase #5	$83.61	7.237%	$89.6609	$89.66	$89.65	$89.70
Purchase #6	$74.27	5.227%	$78.1521	$78.15	$78.15	$78.20
Purchase #7	$169.77	5.732%	$179.5012	$179.50	$179.50	$179.50
7 purchase totals =	$767.42		$820.5007	$820.50	$820.50	$820.60