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	$82.78	7.466%	$88.9604	$88.96	$88.95	$89.00
Purchase #2	$97.70	12.423%	$109.8373	$109.84	$109.85	$109.80
Purchase #3	$73.65	4.386%	$76.8803	$76.88	$76.90	$76.90
Purchase #4	$142.28	6.283%	$151.2195	$151.22	$151.20	$151.20
Purchase #5	$100.77	7.828%	$108.6583	$108.66	$108.65	$108.70
Purchase #6	$121.89	9.789%	$133.8218	$133.82	$133.80	$133.80
Purchase #7	$161.32	3.387%	$166.7839	$166.78	$166.80	$166.80
7 purchase totals =	$780.39		$836.1615	$836.16	$836.15	$836.20