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	$86.41	4.123%	$89.9727	$89.97	$89.95	$90.00
Purchase #2	$69.39	6.849%	$74.1425	$74.14	$74.15	$74.10
Purchase #3	$40.58	11.830%	$45.3806	$45.38	$45.40	$45.40
Purchase #4	$209.30	3.836%	$217.3287	$217.33	$217.35	$217.30
Purchase #5	$72.92	6.138%	$77.3958	$77.40	$77.40	$77.40
Purchase #6	$224.95	9.289%	$245.8456	$245.85	$245.85	$245.80
Purchase #7	$95.99	8.246%	$103.9053	$103.91	$103.90	$103.90
7 purchase totals =	$799.54		$853.9712	$853.98	$854.00	$853.90