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	$194.64	12.472%	$218.9155	$218.92	$218.90	$218.90
Purchase #2	$138.98	4.853%	$145.7247	$145.72	$145.70	$145.70
Purchase #3	$123.72	3.604%	$128.1789	$128.18	$128.20	$128.20
Purchase #4	$156.90	11.238%	$174.5324	$174.53	$174.55	$174.50
Purchase #5	$112.31	10.341%	$123.924	$123.92	$123.90	$123.90
Purchase #6	$198.32	12.829%	$223.7625	$223.76	$223.75	$223.80
Purchase #7	$223.29	10.290%	$246.2665	$246.27	$246.25	$246.30
7 purchase totals =	$1,148.16		$1,261.3045	$1,261.30	$1,261.25	$1,261.30