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	$135.52	3.397%	$140.1236	$140.12	$140.10	$140.10
Purchase #2	$96.44	5.429%	$101.6757	$101.68	$101.70	$101.70
Purchase #3	$70.77	11.615%	$78.9899	$78.99	$79.00	$79.00
Purchase #4	$102.61	9.685%	$112.5478	$112.55	$112.55	$112.50
Purchase #5	$125.47	5.115%	$131.8878	$131.89	$131.90	$131.90
Purchase #6	$118.50	10.821%	$131.3229	$131.32	$131.30	$131.30
Purchase #7	$221.52	4.282%	$231.0055	$231.01	$231.00	$231.00
7 purchase totals =	$870.83		$927.5532	$927.56	$927.55	$927.50