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	$149.44	7.616%	$160.8214	$160.82	$160.80	$160.80
Purchase #2	$65.82	13.799%	$74.9025	$74.90	$74.90	$74.90
Purchase #3	$43.52	11.757%	$48.6366	$48.64	$48.65	$48.60
Purchase #4	$57.25	3.637%	$59.3322	$59.33	$59.35	$59.30
Purchase #5	$116.73	8.712%	$126.8995	$126.90	$126.90	$126.90
Purchase #6	$85.53	4.696%	$89.5465	$89.55	$89.55	$89.50
Purchase #7	$232.67	9.450%	$254.6573	$254.66	$254.65	$254.70
7 purchase totals =	$750.96		$814.7960	$814.80	$814.80	$814.70