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	$110.30	6.474%	$117.4408	$117.44	$117.45	$117.40
Purchase #2	$234.64	9.244%	$256.3301	$256.33	$256.35	$256.30
Purchase #3	$244.77	6.705%	$261.1818	$261.18	$261.20	$261.20
Purchase #4	$82.97	9.402%	$90.7708	$90.77	$90.75	$90.80
Purchase #5	$39.87	11.456%	$44.4375	$44.44	$44.45	$44.40
Purchase #6	$144.76	13.586%	$164.4271	$164.43	$164.45	$164.40
Purchase #7	$171.51	3.804%	$178.0342	$178.03	$178.05	$178.00
7 purchase totals =	$1,028.82		$1,112.6223	$1,112.62	$1,112.70	$1,112.50