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	$51.58	5.833%	$54.5887	$54.59	$54.60	$54.60
Purchase #2	$25.90	4.130%	$26.9697	$26.97	$26.95	$27.00
Purchase #3	$198.50	12.666%	$223.642	$223.64	$223.65	$223.60
Purchase #4	$7.31	5.448%	$7.7082	$7.71	$7.70	$7.70
Purchase #5	$104.30	7.270%	$111.8826	$111.88	$111.90	$111.90
Purchase #6	$46.88	7.300%	$50.3022	$50.30	$50.30	$50.30
Purchase #7	$166.75	9.382%	$182.3945	$182.39	$182.40	$182.40
7 purchase totals =	$601.22		$657.4879	$657.48	$657.50	$657.50