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	$28.80	3.807%	$29.8964	$29.90	$29.90	$29.90
Purchase #2	$211.39	9.468%	$231.4044	$231.40	$231.40	$231.40
Purchase #3	$81.38	9.749%	$89.3137	$89.31	$89.30	$89.30
Purchase #4	$162.57	11.266%	$180.8851	$180.89	$180.90	$180.90
Purchase #5	$108.45	3.338%	$112.0701	$112.07	$112.05	$112.10
Purchase #6	$232.27	10.430%	$256.4958	$256.50	$256.50	$256.50
Purchase #7	$116.94	12.347%	$131.3786	$131.38	$131.40	$131.40
7 purchase totals =	$941.80		$1,031.4441	$1,031.45	$1,031.45	$1,031.50