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	$89.32	11.539%	$99.6266	$99.63	$99.65	$99.60
Purchase #2	$211.37	9.290%	$231.0063	$231.01	$231.00	$231.00
Purchase #3	$147.77	6.599%	$157.5213	$157.52	$157.50	$157.50
Purchase #4	$55.81	6.689%	$59.5431	$59.54	$59.55	$59.50
Purchase #5	$30.29	10.235%	$33.3902	$33.39	$33.40	$33.40
Purchase #6	$142.36	13.519%	$161.6056	$161.61	$161.60	$161.60
Purchase #7	$176.88	5.210%	$186.0954	$186.10	$186.10	$186.10
7 purchase totals =	$853.80		$928.7885	$928.80	$928.80	$928.70