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	$20.61	11.123%	$22.9025	$22.90	$22.90	$22.90
Purchase #2	$72.66	11.245%	$80.8306	$80.83	$80.85	$80.80
Purchase #3	$76.59	12.764%	$86.3659	$86.37	$86.35	$86.40
Purchase #4	$110.46	4.764%	$115.7223	$115.72	$115.70	$115.70
Purchase #5	$188.25	6.602%	$200.6783	$200.68	$200.70	$200.70
Purchase #6	$144.70	7.607%	$155.7073	$155.71	$155.70	$155.70
Purchase #7	$52.32	4.346%	$54.5938	$54.59	$54.60	$54.60
7 purchase totals =	$665.59		$716.8007	$716.80	$716.80	$716.80