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	$48.51	6.365%	$51.5977	$51.60	$51.60	$51.60
Purchase #2	$150.35	4.535%	$157.1684	$157.17	$157.15	$157.20
Purchase #3	$37.83	8.684%	$41.1152	$41.12	$41.10	$41.10
Purchase #4	$235.39	11.797%	$263.159	$263.16	$263.15	$263.20
Purchase #5	$55.41	7.811%	$59.7381	$59.74	$59.75	$59.70
Purchase #6	$146.86	6.863%	$156.939	$156.94	$156.95	$156.90
Purchase #7	$48.83	6.797%	$52.149	$52.15	$52.15	$52.10
7 purchase totals =	$723.18		$781.8664	$781.88	$781.85	$781.80