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	$13.73	6.797%	$14.6632	$14.66	$14.65	$14.70
Purchase #2	$249.87	8.483%	$271.0665	$271.07	$271.05	$271.10
Purchase #3	$249.90	11.732%	$279.2183	$279.22	$279.20	$279.20
Purchase #4	$191.40	12.651%	$215.614	$215.61	$215.60	$215.60
Purchase #5	$37.67	13.407%	$42.7204	$42.72	$42.70	$42.70
Purchase #6	$44.45	8.258%	$48.1207	$48.12	$48.10	$48.10
Purchase #7	$65.25	11.760%	$72.9234	$72.92	$72.90	$72.90
7 purchase totals =	$852.27		$944.3265	$944.32	$944.20	$944.30