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	$128.90	8.136%	$139.3873	$139.39	$139.40	$139.40
Purchase #2	$219.83	8.519%	$238.5573	$238.56	$238.55	$238.60
Purchase #3	$42.76	5.642%	$45.1725	$45.17	$45.15	$45.20
Purchase #4	$165.46	8.730%	$179.9047	$179.90	$179.90	$179.90
Purchase #5	$194.42	13.503%	$220.6725	$220.67	$220.65	$220.70
Purchase #6	$244.75	11.752%	$273.513	$273.51	$273.50	$273.50
Purchase #7	$5.48	7.303%	$5.8802	$5.88	$5.90	$5.90
7 purchase totals =	$1,001.60		$1,103.0875	$1,103.08	$1,103.05	$1,103.20