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	$6.41	8.832%	$6.9761	$6.98	$7.00	$7.00
Purchase #2	$235.40	10.253%	$259.5356	$259.54	$259.55	$259.50
Purchase #3	$195.34	12.842%	$220.4256	$220.43	$220.45	$220.40
Purchase #4	$39.59	9.447%	$43.3301	$43.33	$43.35	$43.30
Purchase #5	$188.46	4.470%	$196.8842	$196.88	$196.90	$196.90
Purchase #6	$220.83	5.215%	$232.3463	$232.35	$232.35	$232.30
Purchase #7	$154.31	11.867%	$172.622	$172.62	$172.60	$172.60
7 purchase totals =	$1,040.34		$1,132.1199	$1,132.13	$1,132.20	$1,132.00