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	$67.33	12.134%	$75.4998	$75.50	$75.50	$75.50
Purchase #2	$149.83	8.392%	$162.4037	$162.40	$162.40	$162.40
Purchase #3	$62.66	8.266%	$67.8395	$67.84	$67.85	$67.80
Purchase #4	$51.50	5.495%	$54.3299	$54.33	$54.35	$54.30
Purchase #5	$244.77	10.508%	$270.4904	$270.49	$270.50	$270.50
Purchase #6	$184.78	7.233%	$198.1451	$198.15	$198.15	$198.10
Purchase #7	$250.72	11.464%	$279.4625	$279.46	$279.45	$279.50
7 purchase totals =	$1,011.59		$1,108.1709	$1,108.17	$1,108.20	$1,108.10