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	$82.76	9.469%	$90.5965	$90.60	$90.60	$90.60
Purchase #2	$142.76	7.306%	$153.19	$153.19	$153.20	$153.20
Purchase #3	$163.48	13.456%	$185.4779	$185.48	$185.50	$185.50
Purchase #4	$210.40	4.744%	$220.3814	$220.38	$220.40	$220.40
Purchase #5	$142.56	11.455%	$158.8902	$158.89	$158.90	$158.90
Purchase #6	$24.44	13.573%	$27.7572	$27.76	$27.75	$27.80
Purchase #7	$78.69	10.479%	$86.9359	$86.94	$86.95	$86.90
7 purchase totals =	$845.09		$923.2291	$923.24	$923.30	$923.30