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	$140.93	3.835%	$146.3347	$146.33	$146.35	$146.30
Purchase #2	$116.72	9.700%	$128.0418	$128.04	$128.05	$128.00
Purchase #3	$53.83	12.172%	$60.3822	$60.38	$60.40	$60.40
Purchase #4	$171.37	12.484%	$192.7638	$192.76	$192.75	$192.80
Purchase #5	$95.95	9.710%	$105.2667	$105.27	$105.25	$105.30
Purchase #6	$76.71	8.222%	$83.0171	$83.02	$83.00	$83.00
Purchase #7	$209.64	5.786%	$221.7698	$221.77	$221.75	$221.80
7 purchase totals =	$865.15		$937.5761	$937.57	$937.55	$937.60