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	$38.66	5.466%	$40.7732	$40.77	$40.75	$40.80
Purchase #2	$136.87	9.700%	$150.1464	$150.15	$150.15	$150.10
Purchase #3	$7.57	4.410%	$7.9038	$7.90	$7.90	$7.90
Purchase #4	$53.27	3.653%	$55.216	$55.22	$55.20	$55.20
Purchase #5	$116.57	10.270%	$128.5417	$128.54	$128.55	$128.50
Purchase #6	$52.64	12.475%	$59.2068	$59.21	$59.20	$59.20
Purchase #7	$224.32	3.820%	$232.889	$232.89	$232.90	$232.90
7 purchase totals =	$629.90		$674.6769	$674.68	$674.65	$674.60