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	$64.65	3.648%	$67.0084	$67.01	$67.00	$67.00
Purchase #2	$247.51	11.253%	$275.3623	$275.36	$275.35	$275.40
Purchase #3	$5.49	13.694%	$6.2418	$6.24	$6.25	$6.20
Purchase #4	$86.40	3.698%	$89.5951	$89.60	$89.60	$89.60
Purchase #5	$33.54	9.399%	$36.6924	$36.69	$36.70	$36.70
Purchase #6	$228.42	12.459%	$256.8788	$256.88	$256.90	$256.90
Purchase #7	$62.29	7.328%	$66.8546	$66.85	$66.85	$66.90
7 purchase totals =	$728.30		$798.6334	$798.63	$798.65	$798.70