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	$59.33	3.792%	$61.5798	$61.58	$61.60	$61.60
Purchase #2	$160.54	13.651%	$182.4553	$182.46	$182.45	$182.50
Purchase #3	$67.25	9.485%	$73.6287	$73.63	$73.65	$73.60
Purchase #4	$37.52	10.552%	$41.4791	$41.48	$41.50	$41.50
Purchase #5	$172.40	6.755%	$184.0456	$184.05	$184.05	$184.00
Purchase #6	$54.46	10.752%	$60.3155	$60.32	$60.30	$60.30
Purchase #7	$7.54	5.437%	$7.9499	$7.95	$7.95	$7.90
7 purchase totals =	$559.04		$611.4539	$611.47	$611.50	$611.40