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	$30.56	8.362%	$33.1154	$33.12	$33.10	$33.10
Purchase #2	$120.82	13.233%	$136.8081	$136.81	$136.80	$136.80
Purchase #3	$36.64	4.308%	$38.2185	$38.22	$38.20	$38.20
Purchase #4	$209.33	6.259%	$222.432	$222.43	$222.45	$222.40
Purchase #5	$78.35	4.543%	$81.9094	$81.91	$81.90	$81.90
Purchase #6	$76.72	9.296%	$83.8519	$83.85	$83.85	$83.90
Purchase #7	$138.42	10.594%	$153.0842	$153.08	$153.10	$153.10
7 purchase totals =	$690.84		$749.4195	$749.42	$749.40	$749.40