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	$234.68	6.715%	$250.4388	$250.44	$250.45	$250.40
Purchase #2	$27.40	11.596%	$30.5773	$30.58	$30.60	$30.60
Purchase #3	$78.47	7.632%	$84.4588	$84.46	$84.45	$84.50
Purchase #4	$56.72	5.601%	$59.8969	$59.90	$59.90	$59.90
Purchase #5	$106.99	6.141%	$113.5603	$113.56	$113.55	$113.60
Purchase #6	$109.84	7.165%	$117.71	$117.71	$117.70	$117.70
Purchase #7	$63.42	12.227%	$71.1744	$71.17	$71.15	$71.20
7 purchase totals =	$677.52		$727.8165	$727.82	$727.80	$727.90