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	$248.51	9.404%	$271.8799	$271.88	$271.90	$271.90
Purchase #2	$234.40	9.551%	$256.7875	$256.79	$256.80	$256.80
Purchase #3	$249.28	8.653%	$270.8502	$270.85	$270.85	$270.90
Purchase #4	$147.76	11.217%	$164.3342	$164.33	$164.35	$164.30
Purchase #5	$248.51	4.423%	$259.5016	$259.50	$259.50	$259.50
Purchase #6	$216.51	6.139%	$229.8015	$229.80	$229.80	$229.80
Purchase #7	$177.71	5.467%	$187.4254	$187.43	$187.45	$187.40
7 purchase totals =	$1,522.68		$1,640.5803	$1,640.58	$1,640.65	$1,640.60