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	$109.56	9.421%	$119.8816	$119.88	$119.90	$119.90
Purchase #2	$165.98	12.528%	$186.774	$186.77	$186.75	$186.80
Purchase #3	$85.83	4.728%	$89.888	$89.89	$89.90	$89.90
Purchase #4	$79.93	13.536%	$90.7493	$90.75	$90.75	$90.70
Purchase #5	$93.41	5.503%	$98.5504	$98.55	$98.55	$98.60
Purchase #6	$236.93	5.419%	$249.7692	$249.77	$249.75	$249.80
Purchase #7	$226.92	6.857%	$242.4799	$242.48	$242.50	$242.50
7 purchase totals =	$998.56		$1,078.0924	$1,078.09	$1,078.10	$1,078.20