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	$51.26	12.844%	$57.8438	$57.84	$57.85	$57.80
Purchase #2	$164.32	11.263%	$182.8274	$182.83	$182.85	$182.80
Purchase #3	$80.59	9.556%	$88.2912	$88.29	$88.30	$88.30
Purchase #4	$131.89	10.544%	$145.7965	$145.80	$145.80	$145.80
Purchase #5	$96.53	6.600%	$102.901	$102.90	$102.90	$102.90
Purchase #6	$121.87	3.641%	$126.3073	$126.31	$126.30	$126.30
Purchase #7	$85.56	7.646%	$92.1019	$92.10	$92.10	$92.10
7 purchase totals =	$732.02		$796.0691	$796.07	$796.10	$796.00