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	$55.48	6.479%	$59.0745	$59.07	$59.05	$59.10
Purchase #2	$54.72	12.588%	$61.6082	$61.61	$61.60	$61.60
Purchase #3	$211.97	3.243%	$218.8442	$218.84	$218.85	$218.80
Purchase #4	$228.64	5.371%	$240.9203	$240.92	$240.90	$240.90
Purchase #5	$137.39	4.448%	$143.5011	$143.50	$143.50	$143.50
Purchase #6	$99.28	5.433%	$104.6739	$104.67	$104.65	$104.70
Purchase #7	$91.95	3.770%	$95.4165	$95.42	$95.40	$95.40
7 purchase totals =	$879.43		$924.0387	$924.03	$923.95	$924.00