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	$106.92	12.212%	$119.9771	$119.98	$120.00	$120.00
Purchase #2	$84.29	12.669%	$94.9687	$94.97	$94.95	$95.00
Purchase #3	$89.86	8.743%	$97.7165	$97.72	$97.70	$97.70
Purchase #4	$79.32	13.205%	$89.7942	$89.79	$89.80	$89.80
Purchase #5	$108.63	6.424%	$115.6084	$115.61	$115.60	$115.60
Purchase #6	$137.77	10.697%	$152.5073	$152.51	$152.50	$152.50
Purchase #7	$39.45	7.286%	$42.3243	$42.32	$42.30	$42.30
7 purchase totals =	$646.24		$712.8965	$712.90	$712.85	$712.90