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	$203.59	7.524%	$218.9081	$218.91	$218.90	$218.90
Purchase #2	$105.73	5.521%	$111.5674	$111.57	$111.55	$111.60
Purchase #3	$112.73	5.393%	$118.8095	$118.81	$118.80	$118.80
Purchase #4	$248.32	6.418%	$264.2572	$264.26	$264.25	$264.30
Purchase #5	$88.96	12.448%	$100.0337	$100.03	$100.05	$100.00
Purchase #6	$178.59	11.279%	$198.7332	$198.73	$198.75	$198.70
Purchase #7	$16.76	6.743%	$17.8901	$17.89	$17.90	$17.90
7 purchase totals =	$954.68		$1,030.1992	$1,030.20	$1,030.20	$1,030.20