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	$25.37	6.572%	$27.0373	$27.04	$27.05	$27.00
Purchase #2	$168.86	12.419%	$189.8307	$189.83	$189.85	$189.80
Purchase #3	$28.55	5.484%	$30.1157	$30.12	$30.10	$30.10
Purchase #4	$76.41	12.310%	$85.8161	$85.82	$85.80	$85.80
Purchase #5	$142.37	7.461%	$152.9922	$152.99	$153.00	$153.00
Purchase #6	$82.29	8.182%	$89.023	$89.02	$89.00	$89.00
Purchase #7	$130.33	12.625%	$146.7842	$146.78	$146.80	$146.80
7 purchase totals =	$654.18		$721.5992	$721.60	$721.60	$721.50