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	$73.56	13.201%	$83.2707	$83.27	$83.25	$83.30
Purchase #2	$11.66	4.772%	$12.2164	$12.22	$12.20	$12.20
Purchase #3	$73.55	7.120%	$78.7868	$78.79	$78.80	$78.80
Purchase #4	$175.45	8.304%	$190.0194	$190.02	$190.00	$190.00
Purchase #5	$148.39	10.619%	$164.1475	$164.15	$164.15	$164.10
Purchase #6	$156.33	9.603%	$171.3424	$171.34	$171.35	$171.30
Purchase #7	$7.85	6.570%	$8.3657	$8.37	$8.35	$8.40
7 purchase totals =	$646.79		$708.1489	$708.16	$708.10	$708.10