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	$52.81	11.771%	$59.0263	$59.03	$59.05	$59.00
Purchase #2	$131.73	9.194%	$143.8413	$143.84	$143.85	$143.80
Purchase #3	$43.41	7.250%	$46.5572	$46.56	$46.55	$46.60
Purchase #4	$213.94	4.606%	$223.7941	$223.79	$223.80	$223.80
Purchase #5	$132.48	13.624%	$150.5291	$150.53	$150.55	$150.50
Purchase #6	$201.82	4.584%	$211.0714	$211.07	$211.05	$211.10
Purchase #7	$144.51	12.737%	$162.9162	$162.92	$162.90	$162.90
7 purchase totals =	$920.70		$997.7356	$997.74	$997.75	$997.70