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	$169.67	4.847%	$177.8939	$177.89	$177.90	$177.90
Purchase #2	$86.80	3.140%	$89.5255	$89.53	$89.55	$89.50
Purchase #3	$163.60	12.590%	$184.1972	$184.20	$184.20	$184.20
Purchase #4	$142.57	6.832%	$152.3104	$152.31	$152.30	$152.30
Purchase #5	$196.43	4.588%	$205.4422	$205.44	$205.45	$205.40
Purchase #6	$6.71	11.798%	$7.5016	$7.50	$7.50	$7.50
Purchase #7	$36.93	13.142%	$41.7833	$41.78	$41.80	$41.80
7 purchase totals =	$802.71		$858.6541	$858.65	$858.70	$858.60