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	$234.94	7.794%	$253.2512	$253.25	$253.25	$253.30
Purchase #2	$162.95	11.201%	$181.202	$181.20	$181.20	$181.20
Purchase #3	$238.64	4.160%	$248.5674	$248.57	$248.55	$248.60
Purchase #4	$161.63	6.611%	$172.3154	$172.32	$172.30	$172.30
Purchase #5	$199.89	4.637%	$209.1589	$209.16	$209.15	$209.20
Purchase #6	$172.82	10.866%	$191.5986	$191.60	$191.60	$191.60
Purchase #7	$240.51	10.450%	$265.6433	$265.64	$265.65	$265.60
7 purchase totals =	$1,411.38		$1,521.7368	$1,521.74	$1,521.70	$1,521.80