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	$250.31	5.586%	$264.2923	$264.29	$264.30	$264.30
Purchase #2	$103.93	6.672%	$110.8642	$110.86	$110.85	$110.90
Purchase #3	$88.89	5.305%	$93.6056	$93.61	$93.60	$93.60
Purchase #4	$83.93	4.247%	$87.4945	$87.49	$87.50	$87.50
Purchase #5	$241.63	12.361%	$271.4979	$271.50	$271.50	$271.50
Purchase #6	$152.86	8.846%	$166.382	$166.38	$166.40	$166.40
Purchase #7	$109.52	8.140%	$118.4349	$118.43	$118.45	$118.40
7 purchase totals =	$1,031.07		$1,112.5714	$1,112.56	$1,112.60	$1,112.60