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	$102.37	12.419%	$115.0833	$115.08	$115.10	$115.10
Purchase #2	$48.74	9.779%	$53.5063	$53.51	$53.50	$53.50
Purchase #3	$196.82	5.858%	$208.3497	$208.35	$208.35	$208.30
Purchase #4	$46.97	9.347%	$51.3603	$51.36	$51.35	$51.40
Purchase #5	$71.27	9.769%	$78.2324	$78.23	$78.25	$78.20
Purchase #6	$56.53	10.194%	$62.2927	$62.29	$62.30	$62.30
Purchase #7	$27.33	4.401%	$28.5328	$28.53	$28.55	$28.50
7 purchase totals =	$550.03		$597.3575	$597.35	$597.40	$597.30