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	$171.71	11.488%	$191.436	$191.44	$191.45	$191.40
Purchase #2	$135.56	10.841%	$150.2561	$150.26	$150.25	$150.30
Purchase #3	$237.74	7.294%	$255.0808	$255.08	$255.10	$255.10
Purchase #4	$64.62	10.869%	$71.6435	$71.64	$71.65	$71.60
Purchase #5	$41.58	8.481%	$45.1064	$45.11	$45.10	$45.10
Purchase #6	$42.68	4.393%	$44.5549	$44.55	$44.55	$44.60
Purchase #7	$207.92	5.769%	$219.9149	$219.91	$219.90	$219.90
7 purchase totals =	$901.81		$977.9926	$977.99	$978.00	$978.00