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	$52.83	5.854%	$55.9227	$55.92	$55.90	$55.90
Purchase #2	$55.94	11.200%	$62.2053	$62.21	$62.20	$62.20
Purchase #3	$92.48	12.217%	$103.7783	$103.78	$103.80	$103.80
Purchase #4	$208.48	9.678%	$228.6567	$228.66	$228.65	$228.70
Purchase #5	$139.59	8.639%	$151.6492	$151.65	$151.65	$151.60
Purchase #6	$210.89	9.220%	$230.3341	$230.33	$230.35	$230.30
Purchase #7	$73.88	11.651%	$82.4878	$82.49	$82.50	$82.50
7 purchase totals =	$834.09		$915.0341	$915.04	$915.05	$915.00