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	$179.73	13.212%	$203.4759	$203.48	$203.50	$203.50
Purchase #2	$30.48	3.450%	$31.5316	$31.53	$31.55	$31.50
Purchase #3	$149.36	6.624%	$159.2536	$159.25	$159.25	$159.30
Purchase #4	$13.59	9.145%	$14.8328	$14.83	$14.85	$14.80
Purchase #5	$159.69	9.142%	$174.2889	$174.29	$174.30	$174.30
Purchase #6	$249.82	12.140%	$280.1481	$280.15	$280.15	$280.10
Purchase #7	$64.89	9.517%	$71.0656	$71.07	$71.05	$71.10
7 purchase totals =	$847.56		$934.5965	$934.60	$934.65	$934.60