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	$101.40	12.825%	$114.4046	$114.40	$114.40	$114.40
Purchase #2	$106.41	6.586%	$113.4182	$113.42	$113.40	$113.40
Purchase #3	$169.77	5.181%	$178.5658	$178.57	$178.55	$178.60
Purchase #4	$167.77	4.770%	$175.7726	$175.77	$175.75	$175.80
Purchase #5	$51.88	8.773%	$56.4314	$56.43	$56.45	$56.40
Purchase #6	$86.48	11.323%	$96.2721	$96.27	$96.25	$96.30
Purchase #7	$42.34	8.411%	$45.9012	$45.90	$45.90	$45.90
7 purchase totals =	$726.05		$780.7659	$780.76	$780.70	$780.80