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	$108.92	13.811%	$123.9629	$123.96	$123.95	$124.00
Purchase #2	$90.52	8.535%	$98.2459	$98.25	$98.25	$98.20
Purchase #3	$57.82	13.786%	$65.7911	$65.79	$65.80	$65.80
Purchase #4	$160.39	11.657%	$179.0867	$179.09	$179.10	$179.10
Purchase #5	$219.65	13.374%	$249.026	$249.03	$249.05	$249.00
Purchase #6	$15.88	6.271%	$16.8758	$16.88	$16.90	$16.90
Purchase #7	$242.34	12.188%	$271.8764	$271.88	$271.90	$271.90
7 purchase totals =	$895.52		$1,004.8648	$1,004.88	$1,004.95	$1,004.90