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	$135.53	5.361%	$142.7958	$142.80	$142.80	$142.80
Purchase #2	$168.70	13.492%	$191.461	$191.46	$191.45	$191.50
Purchase #3	$240.68	5.451%	$253.7995	$253.80	$253.80	$253.80
Purchase #4	$92.85	6.840%	$99.2009	$99.20	$99.20	$99.20
Purchase #5	$234.56	8.277%	$253.9745	$253.97	$253.95	$254.00
Purchase #6	$126.72	11.689%	$141.5323	$141.53	$141.55	$141.50
Purchase #7	$39.29	12.661%	$44.2645	$44.26	$44.25	$44.30
7 purchase totals =	$1,038.33		$1,127.0285	$1,127.02	$1,127.00	$1,127.10