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	$85.37	4.712%	$89.3926	$89.39	$89.40	$89.40
Purchase #2	$112.58	7.130%	$120.607	$120.61	$120.60	$120.60
Purchase #3	$203.88	7.495%	$219.1608	$219.16	$219.15	$219.20
Purchase #4	$63.37	6.578%	$67.5385	$67.54	$67.55	$67.50
Purchase #5	$25.70	3.343%	$26.5592	$26.56	$26.55	$26.60
Purchase #6	$15.46	10.573%	$17.0946	$17.09	$17.10	$17.10
Purchase #7	$66.34	7.242%	$71.1443	$71.14	$71.15	$71.10
7 purchase totals =	$572.70		$611.4970	$611.49	$611.50	$611.50