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	$73.82	13.654%	$83.8994	$83.90	$83.90	$83.90
Purchase #2	$70.96	11.309%	$78.9849	$78.98	$79.00	$79.00
Purchase #3	$172.31	5.620%	$181.9938	$181.99	$182.00	$182.00
Purchase #4	$141.96	13.142%	$160.6164	$160.62	$160.60	$160.60
Purchase #5	$143.70	6.551%	$153.1138	$153.11	$153.10	$153.10
Purchase #6	$173.33	5.437%	$182.754	$182.75	$182.75	$182.80
Purchase #7	$243.73	10.175%	$268.5295	$268.53	$268.55	$268.50
7 purchase totals =	$1,019.81		$1,109.8918	$1,109.88	$1,109.90	$1,109.90