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	$45.63	13.714%	$51.8877	$51.89	$51.90	$51.90
Purchase #2	$188.34	6.436%	$200.4616	$200.46	$200.45	$200.50
Purchase #3	$158.73	12.150%	$178.0157	$178.02	$178.00	$178.00
Purchase #4	$94.37	9.157%	$103.0115	$103.01	$103.00	$103.00
Purchase #5	$48.40	13.722%	$55.0414	$55.04	$55.05	$55.00
Purchase #6	$29.62	7.700%	$31.9007	$31.90	$31.90	$31.90
Purchase #7	$160.91	7.598%	$173.1359	$173.14	$173.15	$173.10
7 purchase totals =	$726.00		$793.4545	$793.46	$793.45	$793.40