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	$38.52	6.479%	$41.0157	$41.02	$41.00	$41.00
Purchase #2	$181.50	9.155%	$198.1163	$198.12	$198.10	$198.10
Purchase #3	$189.50	11.432%	$211.1636	$211.16	$211.15	$211.20
Purchase #4	$166.60	7.787%	$179.5731	$179.57	$179.55	$179.60
Purchase #5	$56.35	4.795%	$59.052	$59.05	$59.05	$59.10
Purchase #6	$54.66	4.321%	$57.0219	$57.02	$57.00	$57.00
Purchase #7	$87.99	13.656%	$100.0059	$100.01	$100.00	$100.00
7 purchase totals =	$775.12		$845.9485	$845.95	$845.85	$846.00