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	$36.50	3.601%	$37.8144	$37.81	$37.80	$37.80
Purchase #2	$113.58	7.828%	$122.471	$122.47	$122.45	$122.50
Purchase #3	$41.84	3.848%	$43.45	$43.45	$43.45	$43.50
Purchase #4	$186.30	5.272%	$196.1217	$196.12	$196.10	$196.10
Purchase #5	$80.69	11.299%	$89.8072	$89.81	$89.80	$89.80
Purchase #6	$192.86	11.107%	$214.281	$214.28	$214.30	$214.30
Purchase #7	$55.75	5.397%	$58.7588	$58.76	$58.75	$58.80
7 purchase totals =	$707.52		$762.7041	$762.70	$762.65	$762.80