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	$153.56	12.274%	$172.408	$172.41	$172.40	$172.40
Purchase #2	$51.53	6.594%	$54.9279	$54.93	$54.95	$54.90
Purchase #3	$237.45	9.552%	$260.1312	$260.13	$260.15	$260.10
Purchase #4	$188.63	6.332%	$200.5741	$200.57	$200.55	$200.60
Purchase #5	$94.42	6.568%	$100.6215	$100.62	$100.60	$100.60
Purchase #6	$86.77	12.846%	$97.9165	$97.92	$97.90	$97.90
Purchase #7	$210.98	7.289%	$226.3583	$226.36	$226.35	$226.40
7 purchase totals =	$1,023.34		$1,112.9375	$1,112.94	$1,112.90	$1,112.90