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	$241.65	5.429%	$254.7692	$254.77	$254.75	$254.80
Purchase #2	$203.95	9.742%	$223.8188	$223.82	$223.80	$223.80
Purchase #3	$41.39	9.541%	$45.339	$45.34	$45.35	$45.30
Purchase #4	$41.60	10.766%	$46.0787	$46.08	$46.10	$46.10
Purchase #5	$87.40	6.263%	$92.8739	$92.87	$92.85	$92.90
Purchase #6	$171.68	8.643%	$186.5183	$186.52	$186.50	$186.50
Purchase #7	$50.63	9.676%	$55.529	$55.53	$55.55	$55.50
7 purchase totals =	$838.30		$904.9269	$904.93	$904.90	$904.90