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	$200.30	12.407%	$225.1512	$225.15	$225.15	$225.20
Purchase #2	$66.30	8.509%	$71.9415	$71.94	$71.95	$71.90
Purchase #3	$31.72	4.413%	$33.1198	$33.12	$33.10	$33.10
Purchase #4	$132.29	7.744%	$142.5345	$142.53	$142.55	$142.50
Purchase #5	$242.96	8.808%	$264.3599	$264.36	$264.35	$264.40
Purchase #6	$39.80	9.546%	$43.5993	$43.60	$43.60	$43.60
Purchase #7	$187.45	8.199%	$202.819	$202.82	$202.80	$202.80
7 purchase totals =	$900.82		$983.5252	$983.52	$983.50	$983.50