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	$237.71	7.604%	$255.7855	$255.79	$255.80	$255.80
Purchase #2	$138.33	8.747%	$150.4297	$150.43	$150.45	$150.40
Purchase #3	$88.87	8.711%	$96.6115	$96.61	$96.60	$96.60
Purchase #4	$246.91	4.537%	$258.1123	$258.11	$258.10	$258.10
Purchase #5	$164.31	10.865%	$182.1623	$182.16	$182.15	$182.20
Purchase #6	$181.88	5.233%	$191.3978	$191.40	$191.40	$191.40
Purchase #7	$221.32	12.745%	$249.5272	$249.53	$249.55	$249.50
7 purchase totals =	$1,279.33		$1,384.0263	$1,384.03	$1,384.05	$1,384.00