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	$23.53	5.782%	$24.8905	$24.89	$24.90	$24.90
Purchase #2	$185.32	5.646%	$195.7832	$195.78	$195.80	$195.80
Purchase #3	$62.54	8.466%	$67.8346	$67.83	$67.85	$67.80
Purchase #4	$162.46	3.330%	$167.8699	$167.87	$167.85	$167.90
Purchase #5	$157.54	6.526%	$167.8211	$167.82	$167.80	$167.80
Purchase #6	$223.87	11.724%	$250.1165	$250.12	$250.10	$250.10
Purchase #7	$199.28	12.288%	$223.7675	$223.77	$223.75	$223.80
7 purchase totals =	$1,014.54		$1,098.0833	$1,098.08	$1,098.05	$1,098.10