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	$29.48	6.659%	$31.4431	$31.44	$31.45	$31.40
Purchase #2	$222.98	12.476%	$250.799	$250.80	$250.80	$250.80
Purchase #3	$238.83	13.837%	$271.8769	$271.88	$271.90	$271.90
Purchase #4	$48.50	8.277%	$52.5143	$52.51	$52.50	$52.50
Purchase #5	$84.90	8.189%	$91.8525	$91.85	$91.85	$91.90
Purchase #6	$102.57	3.527%	$106.1876	$106.19	$106.20	$106.20
Purchase #7	$160.46	13.293%	$181.7899	$181.79	$181.80	$181.80
7 purchase totals =	$887.72		$986.4633	$986.46	$986.50	$986.50