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	$50.53	13.328%	$57.2646	$57.26	$57.25	$57.30
Purchase #2	$158.74	3.501%	$164.2975	$164.30	$164.30	$164.30
Purchase #3	$150.98	11.820%	$168.8258	$168.83	$168.85	$168.80
Purchase #4	$240.98	7.522%	$259.1065	$259.11	$259.10	$259.10
Purchase #5	$198.50	13.572%	$225.4404	$225.44	$225.45	$225.40
Purchase #6	$205.46	12.194%	$230.5138	$230.51	$230.50	$230.50
Purchase #7	$215.67	11.456%	$240.3772	$240.38	$240.40	$240.40
7 purchase totals =	$1,220.86		$1,345.8258	$1,345.83	$1,345.85	$1,345.80