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	$154.90	5.829%	$163.9291	$163.93	$163.95	$163.90
Purchase #2	$46.29	10.469%	$51.1361	$51.14	$51.15	$51.10
Purchase #3	$26.82	4.828%	$28.1149	$28.11	$28.10	$28.10
Purchase #4	$183.63	3.650%	$190.3325	$190.33	$190.35	$190.30
Purchase #5	$225.54	3.411%	$233.2332	$233.23	$233.25	$233.20
Purchase #6	$32.57	8.214%	$35.2453	$35.25	$35.25	$35.20
Purchase #7	$70.75	11.483%	$78.8742	$78.87	$78.85	$78.90
7 purchase totals =	$740.50		$780.8653	$780.86	$780.90	$780.70