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	$93.61	9.800%	$102.7838	$102.78	$102.80	$102.80
Purchase #2	$80.82	3.219%	$83.4216	$83.42	$83.40	$83.40
Purchase #3	$157.57	13.675%	$179.1177	$179.12	$179.10	$179.10
Purchase #4	$163.47	9.808%	$179.5031	$179.50	$179.50	$179.50
Purchase #5	$185.36	6.230%	$196.9079	$196.91	$196.90	$196.90
Purchase #6	$171.53	7.646%	$184.6452	$184.65	$184.65	$184.60
Purchase #7	$126.71	4.707%	$132.6742	$132.67	$132.65	$132.70
7 purchase totals =	$979.07		$1,059.0535	$1,059.05	$1,059.00	$1,059.00