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	$237.62	7.346%	$255.0756	$255.08	$255.10	$255.10
Purchase #2	$242.38	9.134%	$264.519	$264.52	$264.50	$264.50
Purchase #3	$181.89	11.333%	$202.5036	$202.50	$202.50	$202.50
Purchase #4	$54.52	9.601%	$59.7545	$59.75	$59.75	$59.80
Purchase #5	$89.48	4.686%	$93.673	$93.67	$93.65	$93.70
Purchase #6	$122.54	11.435%	$136.5524	$136.55	$136.55	$136.60
Purchase #7	$241.73	10.408%	$266.8893	$266.89	$266.90	$266.90
7 purchase totals =	$1,170.16		$1,278.9674	$1,278.96	$1,278.95	$1,279.10