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	$228.69	9.580%	$250.5985	$250.60	$250.60	$250.60
Purchase #2	$207.38	12.270%	$232.8255	$232.83	$232.85	$232.80
Purchase #3	$105.52	12.675%	$118.8947	$118.89	$118.90	$118.90
Purchase #4	$17.49	6.584%	$18.6415	$18.64	$18.65	$18.60
Purchase #5	$57.41	7.128%	$61.5022	$61.50	$61.50	$61.50
Purchase #6	$40.96	6.197%	$43.4983	$43.50	$43.50	$43.50
Purchase #7	$110.39	6.334%	$117.3821	$117.38	$117.40	$117.40
7 purchase totals =	$767.84		$843.3428	$843.34	$843.40	$843.30