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	$107.52	10.166%	$118.4505	$118.45	$118.45	$118.50
Purchase #2	$220.80	12.802%	$249.0668	$249.07	$249.05	$249.10
Purchase #3	$179.55	6.278%	$190.8221	$190.82	$190.80	$190.80
Purchase #4	$37.95	6.228%	$40.3135	$40.31	$40.30	$40.30
Purchase #5	$209.40	6.473%	$222.9545	$222.95	$222.95	$223.00
Purchase #6	$183.74	6.708%	$196.0653	$196.07	$196.05	$196.10
Purchase #7	$68.85	9.686%	$75.5188	$75.52	$75.50	$75.50
7 purchase totals =	$1,007.81		$1,093.1915	$1,093.19	$1,093.10	$1,093.30