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	$28.89	8.382%	$31.3116	$31.31	$31.30	$31.30
Purchase #2	$119.98	9.167%	$130.9786	$130.98	$131.00	$131.00
Purchase #3	$65.63	4.481%	$68.5709	$68.57	$68.55	$68.60
Purchase #4	$191.90	3.386%	$198.3977	$198.40	$198.40	$198.40
Purchase #5	$152.43	4.592%	$159.4296	$159.43	$159.45	$159.40
Purchase #6	$212.62	8.376%	$230.4291	$230.43	$230.45	$230.40
Purchase #7	$78.44	8.795%	$85.3388	$85.34	$85.35	$85.30
7 purchase totals =	$849.89		$904.4563	$904.46	$904.50	$904.40