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	$170.39	4.365%	$177.8275	$177.83	$177.85	$177.80
Purchase #2	$78.54	5.527%	$82.8809	$82.88	$82.90	$82.90
Purchase #3	$28.27	13.247%	$32.0149	$32.01	$32.00	$32.00
Purchase #4	$17.34	11.392%	$19.3154	$19.32	$19.30	$19.30
Purchase #5	$80.41	9.499%	$88.0481	$88.05	$88.05	$88.00
Purchase #6	$114.60	13.442%	$130.0045	$130.00	$130.00	$130.00
Purchase #7	$82.63	9.553%	$90.5236	$90.52	$90.50	$90.50
7 purchase totals =	$572.18		$620.6149	$620.61	$620.60	$620.50