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	$114.41	12.179%	$128.344	$128.34	$128.35	$128.30
Purchase #2	$52.38	5.717%	$55.3746	$55.37	$55.35	$55.40
Purchase #3	$65.72	11.808%	$73.4802	$73.48	$73.50	$73.50
Purchase #4	$240.31	10.715%	$266.0592	$266.06	$266.05	$266.10
Purchase #5	$174.66	8.859%	$190.1331	$190.13	$190.15	$190.10
Purchase #6	$195.61	10.531%	$216.2097	$216.21	$216.20	$216.20
Purchase #7	$71.73	9.484%	$78.5329	$78.53	$78.55	$78.50
7 purchase totals =	$914.82		$1,008.1337	$1,008.12	$1,008.15	$1,008.10