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	$41.37	3.789%	$42.9375	$42.94	$42.95	$42.90
Purchase #2	$116.76	7.642%	$125.6828	$125.68	$125.70	$125.70
Purchase #3	$174.29	12.383%	$195.8723	$195.87	$195.85	$195.90
Purchase #4	$136.60	11.842%	$152.7762	$152.78	$152.80	$152.80
Purchase #5	$112.70	3.388%	$116.5183	$116.52	$116.50	$116.50
Purchase #6	$158.25	8.377%	$171.5066	$171.51	$171.50	$171.50
Purchase #7	$146.64	12.359%	$164.7632	$164.76	$164.75	$164.80
7 purchase totals =	$886.61		$970.0569	$970.06	$970.05	$970.10