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	$18.86	7.529%	$20.28	$20.28	$20.30	$20.30
Purchase #2	$187.74	9.580%	$205.7255	$205.73	$205.75	$205.70
Purchase #3	$60.27	12.168%	$67.6037	$67.60	$67.60	$67.60
Purchase #4	$170.86	6.683%	$182.2786	$182.28	$182.30	$182.30
Purchase #5	$197.80	5.569%	$208.8155	$208.82	$208.80	$208.80
Purchase #6	$123.97	13.457%	$140.6526	$140.65	$140.65	$140.70
Purchase #7	$37.92	7.752%	$40.8596	$40.86	$40.85	$40.90
7 purchase totals =	$797.42		$866.2155	$866.22	$866.25	$866.30