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	$51.59	6.141%	$54.7581	$54.76	$54.75	$54.80
Purchase #2	$140.77	7.232%	$150.9505	$150.95	$150.95	$151.00
Purchase #3	$159.77	8.229%	$172.9175	$172.92	$172.90	$172.90
Purchase #4	$70.82	11.452%	$78.9303	$78.93	$78.95	$78.90
Purchase #5	$120.50	5.510%	$127.1396	$127.14	$127.15	$127.10
Purchase #6	$191.61	4.340%	$199.9259	$199.93	$199.95	$199.90
Purchase #7	$161.34	6.146%	$171.256	$171.26	$171.25	$171.30
7 purchase totals =	$896.40		$955.8779	$955.89	$955.90	$955.90