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	$116.35	5.843%	$123.1483	$123.15	$123.15	$123.10
Purchase #2	$197.36	6.300%	$209.7937	$209.79	$209.80	$209.80
Purchase #3	$206.26	6.808%	$220.3022	$220.30	$220.30	$220.30
Purchase #4	$13.45	3.307%	$13.8948	$13.89	$13.90	$13.90
Purchase #5	$32.85	5.192%	$34.5556	$34.56	$34.55	$34.60
Purchase #6	$165.81	12.714%	$186.8911	$186.89	$186.90	$186.90
Purchase #7	$108.86	13.144%	$123.1686	$123.17	$123.15	$123.20
7 purchase totals =	$840.94		$911.7543	$911.75	$911.75	$911.80