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	$246.91	6.385%	$262.6752	$262.68	$262.70	$262.70
Purchase #2	$52.84	13.218%	$59.8244	$59.82	$59.80	$59.80
Purchase #3	$18.38	9.641%	$20.152	$20.15	$20.15	$20.20
Purchase #4	$24.98	3.350%	$25.8168	$25.82	$25.80	$25.80
Purchase #5	$140.82	13.534%	$159.8786	$159.88	$159.90	$159.90
Purchase #6	$190.64	3.872%	$198.0216	$198.02	$198.00	$198.00
Purchase #7	$99.55	12.446%	$111.94	$111.94	$111.95	$111.90
7 purchase totals =	$774.12		$838.3086	$838.31	$838.30	$838.30