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	$224.34	8.239%	$242.8234	$242.82	$242.80	$242.80
Purchase #2	$68.65	11.270%	$76.3869	$76.39	$76.40	$76.40
Purchase #3	$96.37	13.463%	$109.3443	$109.34	$109.35	$109.30
Purchase #4	$13.61	11.669%	$15.1982	$15.20	$15.20	$15.20
Purchase #5	$37.45	13.485%	$42.5001	$42.50	$42.50	$42.50
Purchase #6	$95.28	7.591%	$102.5127	$102.51	$102.50	$102.50
Purchase #7	$241.64	11.874%	$270.3323	$270.33	$270.35	$270.30
7 purchase totals =	$777.34		$859.0979	$859.09	$859.10	$859.00