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	$30.60	8.612%	$33.2353	$33.24	$33.25	$33.20
Purchase #2	$151.55	4.168%	$157.8666	$157.87	$157.85	$157.90
Purchase #3	$85.74	3.334%	$88.5986	$88.60	$88.60	$88.60
Purchase #4	$73.33	5.606%	$77.4409	$77.44	$77.45	$77.40
Purchase #5	$194.54	10.311%	$214.599	$214.60	$214.60	$214.60
Purchase #6	$40.60	11.803%	$45.392	$45.39	$45.40	$45.40
Purchase #7	$29.82	6.726%	$31.8257	$31.83	$31.85	$31.80
7 purchase totals =	$606.18		$648.9581	$648.97	$649.00	$648.90