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	$246.96	7.651%	$265.8549	$265.85	$265.85	$265.90
Purchase #2	$114.73	4.502%	$119.8951	$119.90	$119.90	$119.90
Purchase #3	$60.31	5.837%	$63.8303	$63.83	$63.85	$63.80
Purchase #4	$88.63	12.759%	$99.9383	$99.94	$99.95	$99.90
Purchase #5	$73.66	10.846%	$81.6492	$81.65	$81.65	$81.60
Purchase #6	$234.94	9.600%	$257.4942	$257.49	$257.50	$257.50
Purchase #7	$84.50	7.187%	$90.573	$90.57	$90.55	$90.60
7 purchase totals =	$903.73		$979.2350	$979.23	$979.25	$979.20