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	$118.63	10.774%	$131.4112	$131.41	$131.40	$131.40
Purchase #2	$49.48	3.840%	$51.38	$51.38	$51.40	$51.40
Purchase #3	$203.69	7.848%	$219.6756	$219.68	$219.70	$219.70
Purchase #4	$74.80	4.132%	$77.8907	$77.89	$77.90	$77.90
Purchase #5	$42.33	8.103%	$45.76	$45.76	$45.75	$45.80
Purchase #6	$182.87	11.832%	$204.5072	$204.51	$204.50	$204.50
Purchase #7	$55.52	7.747%	$59.8211	$59.82	$59.80	$59.80
7 purchase totals =	$727.32		$790.4458	$790.45	$790.45	$790.50