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	$132.50	5.222%	$139.4192	$139.42	$139.40	$139.40
Purchase #2	$131.99	10.565%	$145.9347	$145.93	$145.95	$145.90
Purchase #3	$33.65	12.166%	$37.7439	$37.74	$37.75	$37.70
Purchase #4	$57.37	9.606%	$62.881	$62.88	$62.90	$62.90
Purchase #5	$70.76	10.376%	$78.1021	$78.10	$78.10	$78.10
Purchase #6	$179.83	11.445%	$200.4115	$200.41	$200.40	$200.40
Purchase #7	$171.71	8.333%	$186.0186	$186.02	$186.00	$186.00
7 purchase totals =	$777.81		$850.5110	$850.50	$850.50	$850.40