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	$59.74	12.857%	$67.4208	$67.42	$67.40	$67.40
Purchase #2	$65.66	8.491%	$71.2352	$71.24	$71.25	$71.20
Purchase #3	$88.90	7.801%	$95.8351	$95.84	$95.85	$95.80
Purchase #4	$147.25	6.186%	$156.3589	$156.36	$156.35	$156.40
Purchase #5	$217.66	6.505%	$231.8188	$231.82	$231.80	$231.80
Purchase #6	$82.99	7.473%	$89.1918	$89.19	$89.20	$89.20
Purchase #7	$111.42	10.393%	$122.9999	$123.00	$123.00	$123.00
7 purchase totals =	$773.62		$834.8605	$834.87	$834.85	$834.80