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	$23.66	6.238%	$25.1359	$25.14	$25.15	$25.10
Purchase #2	$249.87	12.821%	$281.9058	$281.91	$281.90	$281.90
Purchase #3	$201.82	5.793%	$213.5114	$213.51	$213.50	$213.50
Purchase #4	$178.91	6.516%	$190.5678	$190.57	$190.55	$190.60
Purchase #5	$134.53	7.365%	$144.4381	$144.44	$144.45	$144.40
Purchase #6	$86.62	4.218%	$90.2736	$90.27	$90.25	$90.30
Purchase #7	$167.33	12.697%	$188.5759	$188.58	$188.60	$188.60
7 purchase totals =	$1,042.74		$1,134.4085	$1,134.42	$1,134.40	$1,134.40