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	$66.75	6.827%	$71.307	$71.31	$71.30	$71.30
Purchase #2	$122.95	7.632%	$132.3335	$132.33	$132.35	$132.30
Purchase #3	$35.61	4.365%	$37.1644	$37.16	$37.15	$37.20
Purchase #4	$132.38	13.775%	$150.6153	$150.62	$150.60	$150.60
Purchase #5	$186.87	5.372%	$196.9087	$196.91	$196.90	$196.90
Purchase #6	$89.77	8.398%	$97.3089	$97.31	$97.30	$97.30
Purchase #7	$174.95	12.646%	$197.0742	$197.07	$197.05	$197.10
7 purchase totals =	$809.28		$882.7120	$882.71	$882.65	$882.70