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	$93.67	10.189%	$103.214	$103.21	$103.20	$103.20
Purchase #2	$197.45	9.379%	$215.9688	$215.97	$215.95	$216.00
Purchase #3	$63.27	11.394%	$70.479	$70.48	$70.50	$70.50
Purchase #4	$35.38	5.120%	$37.1915	$37.19	$37.20	$37.20
Purchase #5	$79.83	12.356%	$89.6938	$89.69	$89.70	$89.70
Purchase #6	$101.47	3.392%	$104.9119	$104.91	$104.90	$104.90
Purchase #7	$178.62	3.695%	$185.22	$185.22	$185.20	$185.20
7 purchase totals =	$749.69		$806.6790	$806.67	$806.65	$806.70