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	$144.28	13.820%	$164.2195	$164.22	$164.20	$164.20
Purchase #2	$94.46	7.479%	$101.5247	$101.52	$101.50	$101.50
Purchase #3	$213.30	13.695%	$242.5114	$242.51	$242.50	$242.50
Purchase #4	$234.72	9.475%	$256.9597	$256.96	$256.95	$257.00
Purchase #5	$247.52	11.865%	$276.8882	$276.89	$276.90	$276.90
Purchase #6	$110.50	3.627%	$114.5078	$114.51	$114.50	$114.50
Purchase #7	$184.87	11.640%	$206.3889	$206.39	$206.40	$206.40
7 purchase totals =	$1,229.65		$1,363.0002	$1,363.00	$1,362.95	$1,363.00