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	$203.50	10.257%	$224.373	$224.37	$224.35	$224.40
Purchase #2	$189.66	13.658%	$215.5638	$215.56	$215.55	$215.60
Purchase #3	$52.90	6.763%	$56.4776	$56.48	$56.50	$56.50
Purchase #4	$42.48	6.254%	$45.1367	$45.14	$45.15	$45.10
Purchase #5	$74.75	10.227%	$82.3947	$82.39	$82.40	$82.40
Purchase #6	$159.33	7.523%	$171.3164	$171.32	$171.30	$171.30
Purchase #7	$13.61	10.488%	$15.0374	$15.04	$15.05	$15.00
7 purchase totals =	$736.23		$810.2996	$810.30	$810.30	$810.30