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	$48.87	3.851%	$50.752	$50.75	$50.75	$50.80
Purchase #2	$130.68	12.839%	$147.458	$147.46	$147.45	$147.50
Purchase #3	$46.56	3.633%	$48.2515	$48.25	$48.25	$48.30
Purchase #4	$136.66	7.220%	$146.5269	$146.53	$146.55	$146.50
Purchase #5	$158.28	6.411%	$168.4273	$168.43	$168.45	$168.40
Purchase #6	$61.26	10.636%	$67.7756	$67.78	$67.80	$67.80
Purchase #7	$96.92	13.321%	$109.8307	$109.83	$109.85	$109.80
7 purchase totals =	$679.23		$739.0220	$739.03	$739.10	$739.10