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	$39.49	8.681%	$42.9181	$42.92	$42.90	$42.90
Purchase #2	$71.80	8.791%	$78.1119	$78.11	$78.10	$78.10
Purchase #3	$220.47	5.696%	$233.028	$233.03	$233.05	$233.00
Purchase #4	$114.82	4.155%	$119.5908	$119.59	$119.60	$119.60
Purchase #5	$82.70	11.229%	$91.9864	$91.99	$92.00	$92.00
Purchase #6	$104.85	11.400%	$116.8029	$116.80	$116.80	$116.80
Purchase #7	$160.36	5.353%	$168.9441	$168.94	$168.95	$168.90
7 purchase totals =	$794.49		$851.3822	$851.38	$851.40	$851.30