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	$117.59	12.133%	$131.8572	$131.86	$131.85	$131.90
Purchase #2	$20.46	12.261%	$22.9686	$22.97	$22.95	$23.00
Purchase #3	$201.39	6.626%	$214.7341	$214.73	$214.75	$214.70
Purchase #4	$84.32	5.807%	$89.2165	$89.22	$89.20	$89.20
Purchase #5	$74.88	8.737%	$81.4223	$81.42	$81.40	$81.40
Purchase #6	$52.90	4.377%	$55.2154	$55.22	$55.20	$55.20
Purchase #7	$41.78	6.304%	$44.4138	$44.41	$44.40	$44.40
7 purchase totals =	$593.32		$639.8279	$639.83	$639.75	$639.80