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	$158.32	7.567%	$170.3001	$170.30	$170.30	$170.30
Purchase #2	$82.40	7.872%	$88.8865	$88.89	$88.90	$88.90
Purchase #3	$34.36	10.438%	$37.9465	$37.95	$37.95	$37.90
Purchase #4	$105.48	4.379%	$110.099	$110.10	$110.10	$110.10
Purchase #5	$176.40	13.681%	$200.5333	$200.53	$200.55	$200.50
Purchase #6	$66.78	7.563%	$71.8306	$71.83	$71.85	$71.80
Purchase #7	$168.40	6.279%	$178.9738	$178.97	$178.95	$179.00
7 purchase totals =	$792.14		$858.5698	$858.57	$858.60	$858.50