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	$116.38	12.156%	$130.5272	$130.53	$130.55	$130.50
Purchase #2	$112.90	7.756%	$121.6565	$121.66	$121.65	$121.70
Purchase #3	$197.33	12.456%	$221.9094	$221.91	$221.90	$221.90
Purchase #4	$74.30	10.170%	$81.8563	$81.86	$81.85	$81.90
Purchase #5	$114.71	7.666%	$123.5037	$123.50	$123.50	$123.50
Purchase #6	$46.37	10.711%	$51.3367	$51.34	$51.35	$51.30
Purchase #7	$80.26	11.548%	$89.5284	$89.53	$89.55	$89.50
7 purchase totals =	$742.25		$820.3182	$820.33	$820.35	$820.30