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	$73.59	6.668%	$78.497	$78.50	$78.50	$78.50
Purchase #2	$124.32	12.578%	$139.957	$139.96	$139.95	$140.00
Purchase #3	$40.68	6.235%	$43.2164	$43.22	$43.20	$43.20
Purchase #4	$170.80	11.387%	$190.249	$190.25	$190.25	$190.20
Purchase #5	$112.80	4.807%	$118.2223	$118.22	$118.20	$118.20
Purchase #6	$170.85	9.271%	$186.6895	$186.69	$186.70	$186.70
Purchase #7	$160.34	4.814%	$168.0588	$168.06	$168.05	$168.10
7 purchase totals =	$853.38		$924.8900	$924.90	$924.85	$924.90