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	$236.80	3.846%	$245.9073	$245.91	$245.90	$245.90
Purchase #2	$101.92	7.279%	$109.3388	$109.34	$109.35	$109.30
Purchase #3	$166.90	11.256%	$185.6863	$185.69	$185.70	$185.70
Purchase #4	$48.26	4.273%	$50.3221	$50.32	$50.30	$50.30
Purchase #5	$168.37	3.214%	$173.7814	$173.78	$173.80	$173.80
Purchase #6	$34.99	8.108%	$37.827	$37.83	$37.85	$37.80
Purchase #7	$107.63	9.809%	$118.1874	$118.19	$118.20	$118.20
7 purchase totals =	$864.87		$921.0503	$921.06	$921.10	$921.00