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	$77.86	7.326%	$83.564	$83.56	$83.55	$83.60
Purchase #2	$66.64	10.869%	$73.8831	$73.88	$73.90	$73.90
Purchase #3	$221.43	7.573%	$238.1989	$238.20	$238.20	$238.20
Purchase #4	$85.82	5.653%	$90.6714	$90.67	$90.65	$90.70
Purchase #5	$210.45	13.340%	$238.524	$238.52	$238.50	$238.50
Purchase #6	$177.34	4.500%	$185.3203	$185.32	$185.30	$185.30
Purchase #7	$13.40	4.620%	$14.0191	$14.02	$14.00	$14.00
7 purchase totals =	$852.94		$924.1808	$924.17	$924.10	$924.20