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	$242.92	6.729%	$259.2661	$259.27	$259.25	$259.30
Purchase #2	$215.72	6.192%	$229.0774	$229.08	$229.10	$229.10
Purchase #3	$126.71	12.614%	$142.6932	$142.69	$142.70	$142.70
Purchase #4	$30.34	13.589%	$34.4629	$34.46	$34.45	$34.50
Purchase #5	$61.76	9.322%	$67.5173	$67.52	$67.50	$67.50
Purchase #6	$223.96	7.872%	$241.5901	$241.59	$241.60	$241.60
Purchase #7	$222.27	9.727%	$243.8902	$243.89	$243.90	$243.90
7 purchase totals =	$1,123.68		$1,218.4972	$1,218.50	$1,218.50	$1,218.60