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	$44.82	12.244%	$50.3078	$50.31	$50.30	$50.30
Purchase #2	$167.60	7.218%	$179.6974	$179.70	$179.70	$179.70
Purchase #3	$191.46	12.764%	$215.898	$215.90	$215.90	$215.90
Purchase #4	$182.60	6.527%	$194.5183	$194.52	$194.50	$194.50
Purchase #5	$12.82	6.117%	$13.6042	$13.60	$13.60	$13.60
Purchase #6	$153.64	9.544%	$168.3034	$168.30	$168.30	$168.30
Purchase #7	$220.59	12.471%	$248.0998	$248.10	$248.10	$248.10
7 purchase totals =	$973.53		$1,070.4289	$1,070.43	$1,070.40	$1,070.40