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	$40.79	4.305%	$42.546	$42.55	$42.55	$42.50
Purchase #2	$212.60	7.676%	$228.9192	$228.92	$228.90	$228.90
Purchase #3	$166.63	9.690%	$182.7764	$182.78	$182.80	$182.80
Purchase #4	$136.27	4.617%	$142.5616	$142.56	$142.55	$142.60
Purchase #5	$23.99	4.603%	$25.0943	$25.09	$25.10	$25.10
Purchase #6	$57.32	4.178%	$59.7148	$59.71	$59.70	$59.70
Purchase #7	$40.26	12.616%	$45.3392	$45.34	$45.35	$45.30
7 purchase totals =	$677.86		$726.9515	$726.95	$726.95	$726.90