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	$112.76	6.740%	$120.36	$120.36	$120.35	$120.40
Purchase #2	$177.95	11.704%	$198.7773	$198.78	$198.80	$198.80
Purchase #3	$51.80	5.207%	$54.4972	$54.50	$54.50	$54.50
Purchase #4	$56.30	11.331%	$62.6794	$62.68	$62.70	$62.70
Purchase #5	$89.59	11.500%	$99.8929	$99.89	$99.90	$99.90
Purchase #6	$113.96	12.763%	$128.5047	$128.50	$128.50	$128.50
Purchase #7	$102.57	5.750%	$108.4678	$108.47	$108.45	$108.50
7 purchase totals =	$704.93		$773.1793	$773.18	$773.20	$773.30