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	$141.98	10.221%	$156.4918	$156.49	$156.50	$156.50
Purchase #2	$27.45	13.532%	$31.1645	$31.16	$31.15	$31.20
Purchase #3	$172.52	4.273%	$179.8918	$179.89	$179.90	$179.90
Purchase #4	$21.69	7.407%	$23.2966	$23.30	$23.30	$23.30
Purchase #5	$161.63	8.833%	$175.9068	$175.91	$175.90	$175.90
Purchase #6	$71.46	10.488%	$78.9547	$78.95	$78.95	$79.00
Purchase #7	$167.54	11.666%	$187.0852	$187.09	$187.10	$187.10
7 purchase totals =	$764.27		$832.7914	$832.79	$832.80	$832.90