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	$84.78	5.486%	$89.431	$89.43	$89.45	$89.40
Purchase #2	$137.48	9.201%	$150.1295	$150.13	$150.15	$150.10
Purchase #3	$64.46	13.442%	$73.1247	$73.12	$73.10	$73.10
Purchase #4	$191.90	4.867%	$201.2398	$201.24	$201.25	$201.20
Purchase #5	$239.50	3.697%	$248.3543	$248.35	$248.35	$248.40
Purchase #6	$40.60	5.701%	$42.9146	$42.91	$42.90	$42.90
Purchase #7	$181.79	12.156%	$203.8884	$203.89	$203.90	$203.90
7 purchase totals =	$940.51		$1,009.0823	$1,009.07	$1,009.10	$1,009.00