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	$36.57	11.591%	$40.8088	$40.81	$40.80	$40.80
Purchase #2	$85.65	7.339%	$91.9359	$91.94	$91.95	$91.90
Purchase #3	$23.87	13.372%	$27.0619	$27.06	$27.05	$27.10
Purchase #4	$211.89	8.434%	$229.7608	$229.76	$229.75	$229.80
Purchase #5	$103.65	11.453%	$115.521	$115.52	$115.50	$115.50
Purchase #6	$40.53	5.742%	$42.8572	$42.86	$42.85	$42.90
Purchase #7	$174.37	6.834%	$186.2864	$186.29	$186.30	$186.30
7 purchase totals =	$676.53		$734.2320	$734.24	$734.20	$734.30