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	$83.88	5.773%	$88.7224	$88.72	$88.70	$88.70
Purchase #2	$131.50	9.870%	$144.4791	$144.48	$144.50	$144.50
Purchase #3	$138.35	3.278%	$142.8851	$142.89	$142.90	$142.90
Purchase #4	$96.93	12.565%	$109.1093	$109.11	$109.10	$109.10
Purchase #5	$158.78	5.503%	$167.5177	$167.52	$167.50	$167.50
Purchase #6	$65.91	12.749%	$74.3129	$74.31	$74.30	$74.30
Purchase #7	$86.80	4.472%	$90.6817	$90.68	$90.70	$90.70
7 purchase totals =	$762.15		$817.7082	$817.71	$817.70	$817.70