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	$48.58	6.231%	$51.607	$51.61	$51.60	$51.60
Purchase #2	$180.85	5.184%	$190.2253	$190.23	$190.25	$190.20
Purchase #3	$39.30	5.639%	$41.5161	$41.52	$41.50	$41.50
Purchase #4	$162.60	10.282%	$179.3185	$179.32	$179.30	$179.30
Purchase #5	$80.56	6.343%	$85.6699	$85.67	$85.65	$85.70
Purchase #6	$35.99	10.412%	$39.7373	$39.74	$39.75	$39.70
Purchase #7	$16.45	13.871%	$18.7318	$18.73	$18.75	$18.70
7 purchase totals =	$564.33		$606.8059	$606.82	$606.80	$606.70