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	$137.35	9.446%	$150.3241	$150.32	$150.30	$150.30
Purchase #2	$61.83	7.150%	$66.2508	$66.25	$66.25	$66.30
Purchase #3	$95.36	8.148%	$103.1299	$103.13	$103.15	$103.10
Purchase #4	$12.29	9.425%	$13.4483	$13.45	$13.45	$13.40
Purchase #5	$65.52	10.618%	$72.4769	$72.48	$72.50	$72.50
Purchase #6	$223.61	9.704%	$245.3091	$245.31	$245.30	$245.30
Purchase #7	$213.51	11.518%	$238.1021	$238.10	$238.10	$238.10
7 purchase totals =	$809.47		$889.0412	$889.04	$889.05	$889.00