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	$90.87	12.842%	$102.5395	$102.54	$102.55	$102.50
Purchase #2	$34.58	5.497%	$36.4809	$36.48	$36.50	$36.50
Purchase #3	$40.49	13.330%	$45.8873	$45.89	$45.90	$45.90
Purchase #4	$118.87	7.839%	$128.1882	$128.19	$128.20	$128.20
Purchase #5	$151.53	12.850%	$171.0016	$171.00	$171.00	$171.00
Purchase #6	$95.53	10.802%	$105.8492	$105.85	$105.85	$105.80
Purchase #7	$72.85	9.669%	$79.8939	$79.89	$79.90	$79.90
7 purchase totals =	$604.72		$669.8406	$669.84	$669.90	$669.80