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	$242.47	13.472%	$275.1356	$275.14	$275.15	$275.10
Purchase #2	$62.89	7.783%	$67.7847	$67.78	$67.80	$67.80
Purchase #3	$27.29	8.818%	$29.6964	$29.70	$29.70	$29.70
Purchase #4	$41.38	7.244%	$44.3776	$44.38	$44.40	$44.40
Purchase #5	$103.82	8.187%	$112.3197	$112.32	$112.30	$112.30
Purchase #6	$194.59	12.601%	$219.1103	$219.11	$219.10	$219.10
Purchase #7	$248.90	3.851%	$258.4851	$258.49	$258.50	$258.50
7 purchase totals =	$921.34		$1,006.9094	$1,006.92	$1,006.95	$1,006.90