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	$123.50	7.206%	$132.3994	$132.40	$132.40	$132.40
Purchase #2	$113.77	8.211%	$123.1117	$123.11	$123.10	$123.10
Purchase #3	$250.29	4.108%	$260.5719	$260.57	$260.55	$260.60
Purchase #4	$48.59	11.536%	$54.1953	$54.20	$54.20	$54.20
Purchase #5	$222.33	12.811%	$250.8127	$250.81	$250.80	$250.80
Purchase #6	$164.69	8.798%	$179.1794	$179.18	$179.20	$179.20
Purchase #7	$40.47	7.566%	$43.532	$43.53	$43.55	$43.50
7 purchase totals =	$963.64		$1,043.8024	$1,043.80	$1,043.80	$1,043.80