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	$78.50	13.712%	$89.2639	$89.26	$89.25	$89.30
Purchase #2	$249.83	10.280%	$275.5125	$275.51	$275.50	$275.50
Purchase #3	$185.53	12.687%	$209.0682	$209.07	$209.05	$209.10
Purchase #4	$213.36	9.234%	$233.0617	$233.06	$233.05	$233.10
Purchase #5	$63.82	4.210%	$66.5068	$66.51	$66.50	$66.50
Purchase #6	$123.81	13.396%	$140.3956	$140.40	$140.40	$140.40
Purchase #7	$31.98	8.502%	$34.6989	$34.70	$34.70	$34.70
7 purchase totals =	$946.83		$1,048.5076	$1,048.51	$1,048.45	$1,048.60