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	$131.90	5.484%	$139.1334	$139.13	$139.15	$139.10
Purchase #2	$218.51	6.778%	$233.3206	$233.32	$233.30	$233.30
Purchase #3	$40.29	10.228%	$44.4109	$44.41	$44.40	$44.40
Purchase #4	$162.56	10.736%	$180.0124	$180.01	$180.00	$180.00
Purchase #5	$45.70	12.687%	$51.498	$51.50	$51.50	$51.50
Purchase #6	$192.39	10.780%	$213.1296	$213.13	$213.15	$213.10
Purchase #7	$9.78	10.677%	$10.8242	$10.82	$10.80	$10.80
7 purchase totals =	$801.13		$872.3291	$872.32	$872.30	$872.20