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	$109.43	12.708%	$123.3364	$123.34	$123.35	$123.30
Purchase #2	$134.88	8.571%	$146.4406	$146.44	$146.45	$146.40
Purchase #3	$59.45	12.681%	$66.9889	$66.99	$67.00	$67.00
Purchase #4	$195.52	12.250%	$219.4712	$219.47	$219.45	$219.50
Purchase #5	$227.91	10.158%	$251.0611	$251.06	$251.05	$251.10
Purchase #6	$41.70	12.342%	$46.8466	$46.85	$46.85	$46.80
Purchase #7	$203.59	9.199%	$222.3182	$222.32	$222.30	$222.30
7 purchase totals =	$972.48		$1,076.4630	$1,076.47	$1,076.45	$1,076.40