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	$240.76	9.843%	$264.458	$264.46	$264.45	$264.50
Purchase #2	$133.29	4.867%	$139.7772	$139.78	$139.80	$139.80
Purchase #3	$211.28	5.224%	$222.3173	$222.32	$222.30	$222.30
Purchase #4	$185.79	12.350%	$208.7351	$208.74	$208.75	$208.70
Purchase #5	$30.30	6.366%	$32.2289	$32.23	$32.25	$32.20
Purchase #6	$216.55	13.330%	$245.4161	$245.42	$245.40	$245.40
Purchase #7	$138.51	12.670%	$156.0592	$156.06	$156.05	$156.10
7 purchase totals =	$1,156.48		$1,268.9918	$1,269.01	$1,269.00	$1,269.00