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	$42.96	10.781%	$47.5915	$47.59	$47.60	$47.60
Purchase #2	$97.76	12.283%	$109.7679	$109.77	$109.75	$109.80
Purchase #3	$155.73	12.194%	$174.7197	$174.72	$174.70	$174.70
Purchase #4	$140.87	11.510%	$157.0841	$157.08	$157.10	$157.10
Purchase #5	$42.31	10.121%	$46.5922	$46.59	$46.60	$46.60
Purchase #6	$127.57	12.749%	$143.8339	$143.83	$143.85	$143.80
Purchase #7	$142.35	9.150%	$155.375	$155.38	$155.40	$155.40
7 purchase totals =	$749.55		$834.9643	$834.96	$835.00	$835.00