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	$25.47	13.564%	$28.9248	$28.92	$28.90	$28.90
Purchase #2	$124.54	9.241%	$136.0487	$136.05	$136.05	$136.00
Purchase #3	$181.51	9.586%	$198.9095	$198.91	$198.90	$198.90
Purchase #4	$55.38	7.749%	$59.6714	$59.67	$59.65	$59.70
Purchase #5	$104.49	11.378%	$116.3789	$116.38	$116.40	$116.40
Purchase #6	$209.50	10.512%	$231.5226	$231.52	$231.50	$231.50
Purchase #7	$89.40	7.301%	$95.9271	$95.93	$95.95	$95.90
7 purchase totals =	$790.29		$867.3830	$867.38	$867.35	$867.30