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	$119.92	13.865%	$136.5469	$136.55	$136.55	$136.50
Purchase #2	$79.38	5.415%	$83.6784	$83.68	$83.70	$83.70
Purchase #3	$233.61	13.394%	$264.8997	$264.90	$264.90	$264.90
Purchase #4	$82.42	12.201%	$92.4761	$92.48	$92.50	$92.50
Purchase #5	$135.25	5.849%	$143.1608	$143.16	$143.15	$143.20
Purchase #6	$19.37	7.847%	$20.89	$20.89	$20.90	$20.90
Purchase #7	$24.38	4.594%	$25.5	$25.50	$25.50	$25.50
7 purchase totals =	$694.33		$767.1519	$767.16	$767.20	$767.20