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	$41.79	8.481%	$45.3342	$45.33	$45.35	$45.30
Purchase #2	$201.41	10.422%	$222.401	$222.40	$222.40	$222.40
Purchase #3	$191.25	12.549%	$215.25	$215.25	$215.25	$215.30
Purchase #4	$89.84	13.132%	$101.6378	$101.64	$101.65	$101.60
Purchase #5	$160.28	9.502%	$175.5098	$175.51	$175.50	$175.50
Purchase #6	$82.79	10.220%	$91.2511	$91.25	$91.25	$91.30
Purchase #7	$27.39	4.823%	$28.711	$28.71	$28.70	$28.70
7 purchase totals =	$794.75		$880.0949	$880.09	$880.10	$880.10