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	$141.50	3.777%	$146.8445	$146.84	$146.85	$146.80
Purchase #2	$111.53	6.241%	$118.4906	$118.49	$118.50	$118.50
Purchase #3	$82.77	3.360%	$85.5511	$85.55	$85.55	$85.60
Purchase #4	$218.30	11.707%	$243.8564	$243.86	$243.85	$243.90
Purchase #5	$26.77	13.709%	$30.4399	$30.44	$30.45	$30.40
Purchase #6	$111.94	10.564%	$123.7653	$123.77	$123.75	$123.80
Purchase #7	$38.96	4.250%	$40.6158	$40.62	$40.60	$40.60
7 purchase totals =	$731.77		$789.5636	$789.57	$789.55	$789.60