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	$236.84	5.683%	$250.2996	$250.30	$250.30	$250.30
Purchase #2	$232.89	10.208%	$256.6634	$256.66	$256.65	$256.70
Purchase #3	$72.76	11.237%	$80.936	$80.94	$80.95	$80.90
Purchase #4	$36.29	5.156%	$38.1611	$38.16	$38.15	$38.20
Purchase #5	$48.54	6.664%	$51.7747	$51.77	$51.75	$51.80
Purchase #6	$32.73	8.761%	$35.5975	$35.60	$35.60	$35.60
Purchase #7	$77.29	4.688%	$80.9134	$80.91	$80.90	$80.90
7 purchase totals =	$737.34		$794.3457	$794.34	$794.30	$794.40