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	$37.38	11.284%	$41.598	$41.60	$41.60	$41.60
Purchase #2	$57.31	3.279%	$59.1892	$59.19	$59.20	$59.20
Purchase #3	$47.63	8.701%	$51.7743	$51.77	$51.75	$51.80
Purchase #4	$74.69	11.339%	$83.1591	$83.16	$83.15	$83.20
Purchase #5	$16.36	11.854%	$18.2993	$18.30	$18.30	$18.30
Purchase #6	$175.81	8.249%	$190.3126	$190.31	$190.30	$190.30
Purchase #7	$142.62	7.610%	$153.4734	$153.47	$153.45	$153.50
7 purchase totals =	$551.80		$597.8059	$597.80	$597.75	$597.90