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	$238.83	6.436%	$254.2011	$254.20	$254.20	$254.20
Purchase #2	$125.90	8.545%	$136.6582	$136.66	$136.65	$136.70
Purchase #3	$38.96	11.592%	$43.4762	$43.48	$43.50	$43.50
Purchase #4	$76.89	6.465%	$81.8609	$81.86	$81.85	$81.90
Purchase #5	$21.83	11.432%	$24.3256	$24.33	$24.35	$24.30
Purchase #6	$219.59	12.849%	$247.8051	$247.81	$247.80	$247.80
Purchase #7	$190.83	10.825%	$211.4873	$211.49	$211.50	$211.50
7 purchase totals =	$912.83		$999.8144	$999.83	$999.85	$999.90