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	$193.50	9.422%	$211.7316	$211.73	$211.75	$211.70
Purchase #2	$46.85	6.760%	$50.0171	$50.02	$50.00	$50.00
Purchase #3	$29.55	5.721%	$31.2406	$31.24	$31.25	$31.20
Purchase #4	$101.47	10.584%	$112.2096	$112.21	$112.20	$112.20
Purchase #5	$42.73	7.135%	$45.7788	$45.78	$45.80	$45.80
Purchase #6	$121.78	12.571%	$137.089	$137.09	$137.10	$137.10
Purchase #7	$73.41	8.195%	$79.4259	$79.43	$79.45	$79.40
7 purchase totals =	$609.29		$667.4926	$667.50	$667.55	$667.40