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	$31.37	7.390%	$33.6882	$33.69	$33.70	$33.70
Purchase #2	$60.73	11.834%	$67.9168	$67.92	$67.90	$67.90
Purchase #3	$146.47	10.288%	$161.5388	$161.54	$161.55	$161.50
Purchase #4	$163.29	13.597%	$185.4925	$185.49	$185.50	$185.50
Purchase #5	$155.94	5.690%	$164.813	$164.81	$164.80	$164.80
Purchase #6	$38.51	11.822%	$43.0627	$43.06	$43.05	$43.10
Purchase #7	$111.57	10.292%	$123.0528	$123.05	$123.05	$123.10
7 purchase totals =	$707.88		$779.5648	$779.56	$779.55	$779.60