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	$81.54	9.680%	$89.4331	$89.43	$89.45	$89.40
Purchase #2	$175.72	13.423%	$199.3069	$199.31	$199.30	$199.30
Purchase #3	$226.55	5.193%	$238.3147	$238.31	$238.30	$238.30
Purchase #4	$25.43	4.725%	$26.6316	$26.63	$26.65	$26.60
Purchase #5	$73.71	6.872%	$78.7754	$78.78	$78.80	$78.80
Purchase #6	$207.59	3.693%	$215.2563	$215.26	$215.25	$215.30
Purchase #7	$12.76	10.873%	$14.1474	$14.15	$14.15	$14.10
7 purchase totals =	$803.30		$861.8654	$861.87	$861.90	$861.80