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	$40.56	3.429%	$41.9508	$41.95	$41.95	$42.00
Purchase #2	$79.30	7.751%	$85.4465	$85.45	$85.45	$85.40
Purchase #3	$36.37	12.528%	$40.9264	$40.93	$40.95	$40.90
Purchase #4	$137.94	10.111%	$151.8871	$151.89	$151.90	$151.90
Purchase #5	$217.32	11.543%	$242.4052	$242.41	$242.40	$242.40
Purchase #6	$37.27	13.182%	$42.1829	$42.18	$42.20	$42.20
Purchase #7	$209.80	9.849%	$230.4632	$230.46	$230.45	$230.50
7 purchase totals =	$758.56		$835.2621	$835.27	$835.30	$835.30