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	$142.90	5.830%	$151.2311	$151.23	$151.25	$151.20
Purchase #2	$75.56	13.264%	$85.5823	$85.58	$85.60	$85.60
Purchase #3	$241.78	11.679%	$270.0175	$270.02	$270.00	$270.00
Purchase #4	$43.86	10.306%	$48.3802	$48.38	$48.40	$48.40
Purchase #5	$217.57	9.222%	$237.6343	$237.63	$237.65	$237.60
Purchase #6	$29.35	10.803%	$32.5207	$32.52	$32.50	$32.50
Purchase #7	$28.29	5.469%	$29.8372	$29.84	$29.85	$29.80
7 purchase totals =	$779.31		$855.2033	$855.20	$855.25	$855.10