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	$231.82	5.508%	$244.5886	$244.59	$244.60	$244.60
Purchase #2	$231.57	7.481%	$248.8938	$248.89	$248.90	$248.90
Purchase #3	$37.77	10.663%	$41.7974	$41.80	$41.80	$41.80
Purchase #4	$35.28	13.402%	$40.0082	$40.01	$40.00	$40.00
Purchase #5	$144.55	9.288%	$157.9758	$157.98	$158.00	$158.00
Purchase #6	$150.36	8.412%	$163.0083	$163.01	$163.00	$163.00
Purchase #7	$38.98	9.299%	$42.6048	$42.60	$42.60	$42.60
7 purchase totals =	$870.33		$938.8769	$938.88	$938.90	$938.90