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	$22.91	9.661%	$25.1233	$25.12	$25.10	$25.10
Purchase #2	$148.67	11.342%	$165.5322	$165.53	$165.55	$165.50
Purchase #3	$238.36	9.561%	$261.1496	$261.15	$261.15	$261.10
Purchase #4	$30.81	3.317%	$31.832	$31.83	$31.85	$31.80
Purchase #5	$97.88	11.839%	$109.468	$109.47	$109.45	$109.50
Purchase #6	$11.31	11.462%	$12.6064	$12.61	$12.60	$12.60
Purchase #7	$237.88	5.190%	$250.226	$250.23	$250.25	$250.20
7 purchase totals =	$787.82		$855.9375	$855.94	$855.95	$855.80