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	$37.25	12.356%	$41.8526	$41.85	$41.85	$41.90
Purchase #2	$229.88	10.386%	$253.7553	$253.76	$253.75	$253.80
Purchase #3	$165.77	4.392%	$173.0506	$173.05	$173.05	$173.10
Purchase #4	$174.57	12.540%	$196.4611	$196.46	$196.45	$196.50
Purchase #5	$56.41	11.671%	$62.9936	$62.99	$63.00	$63.00
Purchase #6	$172.86	5.861%	$182.9913	$182.99	$183.00	$183.00
Purchase #7	$112.73	5.629%	$119.0756	$119.08	$119.10	$119.10
7 purchase totals =	$949.47		$1,030.1801	$1,030.18	$1,030.20	$1,030.40