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	$111.36	11.245%	$123.8824	$123.88	$123.90	$123.90
Purchase #2	$148.48	7.781%	$160.0332	$160.03	$160.05	$160.00
Purchase #3	$234.85	3.438%	$242.9241	$242.92	$242.90	$242.90
Purchase #4	$132.80	13.355%	$150.5354	$150.54	$150.55	$150.50
Purchase #5	$207.34	12.652%	$233.5727	$233.57	$233.55	$233.60
Purchase #6	$132.35	3.434%	$136.8949	$136.89	$136.90	$136.90
Purchase #7	$62.74	7.375%	$67.3671	$67.37	$67.35	$67.40
7 purchase totals =	$1,029.92		$1,115.2098	$1,115.20	$1,115.20	$1,115.20