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	$80.58	3.390%	$83.3117	$83.31	$83.30	$83.30
Purchase #2	$157.79	10.802%	$174.8345	$174.83	$174.85	$174.80
Purchase #3	$41.36	5.365%	$43.579	$43.58	$43.60	$43.60
Purchase #4	$177.96	10.416%	$196.4963	$196.50	$196.50	$196.50
Purchase #5	$57.31	12.525%	$64.4881	$64.49	$64.50	$64.50
Purchase #6	$25.32	4.223%	$26.3893	$26.39	$26.40	$26.40
Purchase #7	$219.70	13.225%	$248.7553	$248.76	$248.75	$248.80
7 purchase totals =	$760.02		$837.8542	$837.86	$837.90	$837.90