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	$68.78	13.767%	$78.2489	$78.25	$78.25	$78.20
Purchase #2	$89.31	10.297%	$98.5063	$98.51	$98.50	$98.50
Purchase #3	$165.88	9.596%	$181.7978	$181.80	$181.80	$181.80
Purchase #4	$7.56	3.104%	$7.7947	$7.79	$7.80	$7.80
Purchase #5	$174.69	6.666%	$186.3348	$186.33	$186.35	$186.30
Purchase #6	$161.25	12.205%	$180.9306	$180.93	$180.95	$180.90
Purchase #7	$154.88	12.571%	$174.35	$174.35	$174.35	$174.40
7 purchase totals =	$822.35		$907.9631	$907.96	$908.00	$907.90