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	$230.75	10.270%	$254.448	$254.45	$254.45	$254.40
Purchase #2	$188.37	4.266%	$196.4059	$196.41	$196.40	$196.40
Purchase #3	$83.98	6.293%	$89.2649	$89.26	$89.25	$89.30
Purchase #4	$128.95	5.538%	$136.0913	$136.09	$136.10	$136.10
Purchase #5	$7.67	7.744%	$8.264	$8.26	$8.25	$8.30
Purchase #6	$243.90	12.626%	$274.6948	$274.69	$274.70	$274.70
Purchase #7	$49.48	9.681%	$54.2702	$54.27	$54.25	$54.30
7 purchase totals =	$933.10		$1,013.4391	$1,013.43	$1,013.40	$1,013.50