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	$80.82	12.468%	$90.8966	$90.90	$90.90	$90.90
Purchase #2	$44.32	11.476%	$49.4062	$49.41	$49.40	$49.40
Purchase #3	$168.33	7.471%	$180.9059	$180.91	$180.90	$180.90
Purchase #4	$126.47	11.292%	$140.751	$140.75	$140.75	$140.80
Purchase #5	$90.50	3.621%	$93.777	$93.78	$93.80	$93.80
Purchase #6	$119.37	9.333%	$130.5108	$130.51	$130.50	$130.50
Purchase #7	$102.47	7.381%	$110.0333	$110.03	$110.05	$110.00
7 purchase totals =	$732.28		$796.2808	$796.29	$796.30	$796.30