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	$121.88	5.678%	$128.8003	$128.80	$128.80	$128.80
Purchase #2	$247.39	13.198%	$280.0405	$280.04	$280.05	$280.00
Purchase #3	$240.33	4.146%	$250.2941	$250.29	$250.30	$250.30
Purchase #4	$234.97	7.790%	$253.2742	$253.27	$253.25	$253.30
Purchase #5	$34.48	9.625%	$37.7987	$37.80	$37.80	$37.80
Purchase #6	$160.46	11.785%	$179.3702	$179.37	$179.35	$179.40
Purchase #7	$50.60	8.257%	$54.778	$54.78	$54.80	$54.80
7 purchase totals =	$1,090.11		$1,184.3560	$1,184.35	$1,184.35	$1,184.40