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	$178.34	5.337%	$187.858	$187.86	$187.85	$187.90
Purchase #2	$52.64	13.637%	$59.8185	$59.82	$59.80	$59.80
Purchase #3	$167.47	8.706%	$182.0499	$182.05	$182.05	$182.00
Purchase #4	$43.54	4.865%	$45.6582	$45.66	$45.65	$45.70
Purchase #5	$158.58	6.721%	$169.2382	$169.24	$169.25	$169.20
Purchase #6	$106.60	5.814%	$112.7977	$112.80	$112.80	$112.80
Purchase #7	$115.45	7.846%	$124.5082	$124.51	$124.50	$124.50
7 purchase totals =	$822.62		$881.9287	$881.94	$881.90	$881.90