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	$50.66	3.792%	$52.581	$52.58	$52.60	$52.60
Purchase #2	$142.93	9.619%	$156.6784	$156.68	$156.70	$156.70
Purchase #3	$217.58	12.774%	$245.3737	$245.37	$245.35	$245.40
Purchase #4	$159.31	13.112%	$180.1987	$180.20	$180.20	$180.20
Purchase #5	$210.83	13.152%	$238.5584	$238.56	$238.55	$238.60
Purchase #6	$6.54	9.308%	$7.1487	$7.15	$7.15	$7.10
Purchase #7	$37.30	8.208%	$40.3616	$40.36	$40.35	$40.40
7 purchase totals =	$825.15		$920.9005	$920.90	$920.90	$921.00