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	$37.29	13.461%	$42.3096	$42.31	$42.30	$42.30
Purchase #2	$209.83	13.554%	$238.2704	$238.27	$238.25	$238.30
Purchase #3	$197.47	9.289%	$215.813	$215.81	$215.80	$215.80
Purchase #4	$61.48	8.620%	$66.7796	$66.78	$66.80	$66.80
Purchase #5	$222.47	4.697%	$232.9194	$232.92	$232.90	$232.90
Purchase #6	$105.49	8.414%	$114.3659	$114.37	$114.35	$114.40
Purchase #7	$187.51	9.874%	$206.0247	$206.02	$206.00	$206.00
7 purchase totals =	$1,021.54		$1,116.4826	$1,116.48	$1,116.40	$1,116.50