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	$155.57	5.654%	$164.3659	$164.37	$164.35	$164.40
Purchase #2	$147.34	10.221%	$162.3996	$162.40	$162.40	$162.40
Purchase #3	$10.38	5.119%	$10.9114	$10.91	$10.90	$10.90
Purchase #4	$121.38	3.210%	$125.2763	$125.28	$125.30	$125.30
Purchase #5	$42.94	6.479%	$45.7221	$45.72	$45.70	$45.70
Purchase #6	$102.90	9.490%	$112.6652	$112.67	$112.65	$112.70
Purchase #7	$18.64	4.339%	$19.4488	$19.45	$19.45	$19.40
7 purchase totals =	$599.15		$640.7893	$640.80	$640.75	$640.80