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	$84.51	5.790%	$89.4031	$89.40	$89.40	$89.40
Purchase #2	$244.86	4.318%	$255.4331	$255.43	$255.45	$255.40
Purchase #3	$14.98	13.534%	$17.0074	$17.01	$17.00	$17.00
Purchase #4	$96.74	9.368%	$105.8026	$105.80	$105.80	$105.80
Purchase #5	$75.84	8.777%	$82.4965	$82.50	$82.50	$82.50
Purchase #6	$211.25	8.562%	$229.3372	$229.34	$229.35	$229.30
Purchase #7	$160.70	11.404%	$179.0262	$179.03	$179.05	$179.00
7 purchase totals =	$888.88		$958.5061	$958.51	$958.55	$958.40