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	$128.83	11.859%	$144.1079	$144.11	$144.10	$144.10
Purchase #2	$216.53	9.523%	$237.1502	$237.15	$237.15	$237.20
Purchase #3	$201.67	11.191%	$224.2389	$224.24	$224.25	$224.20
Purchase #4	$180.30	3.457%	$186.533	$186.53	$186.55	$186.50
Purchase #5	$198.95	3.403%	$205.7203	$205.72	$205.70	$205.70
Purchase #6	$54.78	9.398%	$59.9282	$59.93	$59.95	$59.90
Purchase #7	$39.80	8.787%	$43.2972	$43.30	$43.30	$43.30
7 purchase totals =	$1,020.86		$1,100.9757	$1,100.98	$1,101.00	$1,100.90