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	$206.86	8.871%	$225.2106	$225.21	$225.20	$225.20
Purchase #2	$135.79	9.480%	$148.6629	$148.66	$148.65	$148.70
Purchase #3	$130.76	10.263%	$144.1799	$144.18	$144.20	$144.20
Purchase #4	$219.50	13.509%	$249.1523	$249.15	$249.15	$249.20
Purchase #5	$80.35	10.857%	$89.0736	$89.07	$89.05	$89.10
Purchase #6	$88.89	11.753%	$99.3372	$99.34	$99.35	$99.30
Purchase #7	$238.86	10.331%	$263.5366	$263.54	$263.55	$263.50
7 purchase totals =	$1,101.01		$1,219.1531	$1,219.15	$1,219.15	$1,219.20