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	$44.96	8.752%	$48.8949	$48.89	$48.90	$48.90
Purchase #2	$172.43	7.173%	$184.7984	$184.80	$184.80	$184.80
Purchase #3	$248.91	10.520%	$275.0953	$275.10	$275.10	$275.10
Purchase #4	$139.51	8.151%	$150.8815	$150.88	$150.90	$150.90
Purchase #5	$126.76	13.112%	$143.3808	$143.38	$143.40	$143.40
Purchase #6	$74.44	10.542%	$82.2875	$82.29	$82.30	$82.30
Purchase #7	$59.37	3.426%	$61.404	$61.40	$61.40	$61.40
7 purchase totals =	$866.38		$946.7424	$946.74	$946.80	$946.80