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	$143.50	5.799%	$151.8216	$151.82	$151.80	$151.80
Purchase #2	$241.90	3.592%	$250.589	$250.59	$250.60	$250.60
Purchase #3	$244.71	4.504%	$255.7317	$255.73	$255.75	$255.70
Purchase #4	$33.77	11.412%	$37.6238	$37.62	$37.60	$37.60
Purchase #5	$219.47	4.435%	$229.2035	$229.20	$229.20	$229.20
Purchase #6	$218.94	10.504%	$241.9375	$241.94	$241.95	$241.90
Purchase #7	$88.49	5.860%	$93.6755	$93.68	$93.70	$93.70
7 purchase totals =	$1,190.78		$1,260.5826	$1,260.58	$1,260.60	$1,260.50