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	$157.41	3.266%	$162.551	$162.55	$162.55	$162.60
Purchase #2	$106.39	3.173%	$109.7658	$109.77	$109.75	$109.80
Purchase #3	$96.41	9.507%	$105.5757	$105.58	$105.60	$105.60
Purchase #4	$99.77	8.710%	$108.46	$108.46	$108.45	$108.50
Purchase #5	$141.87	4.394%	$148.1038	$148.10	$148.10	$148.10
Purchase #6	$157.77	8.526%	$171.2215	$171.22	$171.20	$171.20
Purchase #7	$29.79	7.235%	$31.9453	$31.95	$31.95	$31.90
7 purchase totals =	$789.41		$837.6231	$837.63	$837.60	$837.70