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	$102.32	13.492%	$116.125	$116.13	$116.15	$116.10
Purchase #2	$143.86	9.637%	$157.7238	$157.72	$157.70	$157.70
Purchase #3	$78.64	5.538%	$82.9951	$83.00	$83.00	$83.00
Purchase #4	$135.94	13.156%	$153.8243	$153.82	$153.80	$153.80
Purchase #5	$50.41	5.710%	$53.2884	$53.29	$53.30	$53.30
Purchase #6	$195.44	13.665%	$222.1469	$222.15	$222.15	$222.10
Purchase #7	$142.89	13.507%	$162.1902	$162.19	$162.20	$162.20
7 purchase totals =	$849.50		$948.2937	$948.30	$948.30	$948.20