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	$139.84	12.174%	$156.8641	$156.86	$156.85	$156.90
Purchase #2	$151.30	5.288%	$159.3007	$159.30	$159.30	$159.30
Purchase #3	$124.94	4.123%	$130.0913	$130.09	$130.10	$130.10
Purchase #4	$44.98	5.850%	$47.6113	$47.61	$47.60	$47.60
Purchase #5	$21.96	3.853%	$22.8061	$22.81	$22.80	$22.80
Purchase #6	$79.76	3.598%	$82.6298	$82.63	$82.65	$82.60
Purchase #7	$159.34	7.638%	$171.5104	$171.51	$171.50	$171.50
7 purchase totals =	$722.12		$770.8137	$770.81	$770.80	$770.80