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	$127.26	9.439%	$139.2721	$139.27	$139.25	$139.30
Purchase #2	$147.53	11.499%	$164.4945	$164.49	$164.50	$164.50
Purchase #3	$154.61	3.441%	$159.9301	$159.93	$159.95	$159.90
Purchase #4	$221.67	8.601%	$240.7358	$240.74	$240.75	$240.70
Purchase #5	$104.33	7.783%	$112.45	$112.45	$112.45	$112.50
Purchase #6	$65.94	9.551%	$72.2379	$72.24	$72.25	$72.20
Purchase #7	$20.85	7.141%	$22.3389	$22.34	$22.35	$22.30
7 purchase totals =	$842.19		$911.4593	$911.46	$911.50	$911.40