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	$44.39	8.817%	$48.3039	$48.30	$48.30	$48.30
Purchase #2	$66.81	9.528%	$73.1757	$73.18	$73.20	$73.20
Purchase #3	$38.59	12.180%	$43.2903	$43.29	$43.30	$43.30
Purchase #4	$120.91	8.244%	$130.8778	$130.88	$130.90	$130.90
Purchase #5	$36.28	11.271%	$40.3691	$40.37	$40.35	$40.40
Purchase #6	$55.32	4.625%	$57.8786	$57.88	$57.90	$57.90
Purchase #7	$225.74	4.294%	$235.4333	$235.43	$235.45	$235.40
7 purchase totals =	$588.04		$629.3287	$629.33	$629.40	$629.40