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	$5.97	5.732%	$6.3122	$6.31	$6.30	$6.30
Purchase #2	$143.80	6.373%	$152.9644	$152.96	$152.95	$153.00
Purchase #3	$67.28	7.318%	$72.2036	$72.20	$72.20	$72.20
Purchase #4	$48.81	13.619%	$55.4574	$55.46	$55.45	$55.50
Purchase #5	$144.64	6.315%	$153.774	$153.77	$153.75	$153.80
Purchase #6	$140.27	7.495%	$150.7832	$150.78	$150.80	$150.80
Purchase #7	$105.90	13.817%	$120.5322	$120.53	$120.55	$120.50
7 purchase totals =	$656.67		$712.0270	$712.01	$712.00	$712.10