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	$77.75	4.792%	$81.4758	$81.48	$81.50	$81.50
Purchase #2	$185.64	12.644%	$209.1123	$209.11	$209.10	$209.10
Purchase #3	$184.78	6.269%	$196.3639	$196.36	$196.35	$196.40
Purchase #4	$157.43	10.118%	$173.3588	$173.36	$173.35	$173.40
Purchase #5	$78.92	8.208%	$85.3978	$85.40	$85.40	$85.40
Purchase #6	$133.89	3.129%	$138.0794	$138.08	$138.10	$138.10
Purchase #7	$171.75	6.713%	$183.2796	$183.28	$183.30	$183.30
7 purchase totals =	$990.16		$1,067.0676	$1,067.07	$1,067.10	$1,067.20