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	$223.30	10.139%	$245.9404	$245.94	$245.95	$245.90
Purchase #2	$159.71	13.604%	$181.4369	$181.44	$181.45	$181.40
Purchase #3	$190.46	4.136%	$198.3374	$198.34	$198.35	$198.30
Purchase #4	$43.49	3.125%	$44.8491	$44.85	$44.85	$44.80
Purchase #5	$85.47	6.393%	$90.9341	$90.93	$90.95	$90.90
Purchase #6	$19.54	3.562%	$20.236	$20.24	$20.25	$20.20
Purchase #7	$64.45	13.840%	$73.3699	$73.37	$73.35	$73.40
7 purchase totals =	$786.42		$855.1038	$855.11	$855.15	$854.90