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	$37.77	7.817%	$40.7225	$40.72	$40.70	$40.70
Purchase #2	$40.44	4.689%	$42.3362	$42.34	$42.35	$42.30
Purchase #3	$75.29	9.616%	$82.5299	$82.53	$82.55	$82.50
Purchase #4	$202.39	5.629%	$213.7825	$213.78	$213.80	$213.80
Purchase #5	$8.50	10.727%	$9.4118	$9.41	$9.40	$9.40
Purchase #6	$220.39	8.809%	$239.8042	$239.80	$239.80	$239.80
Purchase #7	$68.28	5.418%	$71.9794	$71.98	$72.00	$72.00
7 purchase totals =	$653.06		$700.5665	$700.56	$700.60	$700.50