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	$69.97	12.683%	$78.8443	$78.84	$78.85	$78.80
Purchase #2	$108.65	4.682%	$113.737	$113.74	$113.75	$113.70
Purchase #3	$40.69	7.183%	$43.6128	$43.61	$43.60	$43.60
Purchase #4	$58.97	4.435%	$61.5853	$61.59	$61.60	$61.60
Purchase #5	$113.50	8.644%	$123.3109	$123.31	$123.30	$123.30
Purchase #6	$135.28	7.839%	$145.8846	$145.88	$145.90	$145.90
Purchase #7	$216.67	3.196%	$223.5948	$223.59	$223.60	$223.60
7 purchase totals =	$743.73		$790.5697	$790.56	$790.60	$790.50