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	$240.27	6.443%	$255.7506	$255.75	$255.75	$255.80
Purchase #2	$245.40	11.141%	$272.74	$272.74	$272.75	$272.70
Purchase #3	$83.54	12.374%	$93.8772	$93.88	$93.90	$93.90
Purchase #4	$62.48	7.620%	$67.241	$67.24	$67.25	$67.20
Purchase #5	$46.29	4.670%	$48.4517	$48.45	$48.45	$48.50
Purchase #6	$128.69	10.864%	$142.6709	$142.67	$142.65	$142.70
Purchase #7	$120.65	8.796%	$131.2624	$131.26	$131.25	$131.30
7 purchase totals =	$927.32		$1,011.9938	$1,011.99	$1,012.00	$1,012.10