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	$52.87	12.476%	$59.4661	$59.47	$59.45	$59.50
Purchase #2	$240.78	12.221%	$270.2057	$270.21	$270.20	$270.20
Purchase #3	$49.46	4.674%	$51.7718	$51.77	$51.75	$51.80
Purchase #4	$20.82	13.487%	$23.628	$23.63	$23.65	$23.60
Purchase #5	$171.70	7.541%	$184.6479	$184.65	$184.65	$184.60
Purchase #6	$7.42	4.862%	$7.7808	$7.78	$7.80	$7.80
Purchase #7	$52.40	8.792%	$57.007	$57.01	$57.00	$57.00
7 purchase totals =	$595.45		$654.5073	$654.52	$654.50	$654.50