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	$137.70	10.818%	$152.5964	$152.60	$152.60	$152.60
Purchase #2	$26.74	5.310%	$28.1599	$28.16	$28.15	$28.20
Purchase #3	$42.27	3.695%	$43.8319	$43.83	$43.85	$43.80
Purchase #4	$216.87	8.184%	$234.6186	$234.62	$234.60	$234.60
Purchase #5	$132.47	7.848%	$142.8662	$142.87	$142.85	$142.90
Purchase #6	$241.94	3.407%	$250.1829	$250.18	$250.20	$250.20
Purchase #7	$36.29	10.229%	$40.0021	$40.00	$40.00	$40.00
7 purchase totals =	$834.28		$892.2580	$892.26	$892.25	$892.30