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	$14.91	3.739%	$15.4675	$15.47	$15.45	$15.50
Purchase #2	$97.50	8.298%	$105.5906	$105.59	$105.60	$105.60
Purchase #3	$27.62	4.722%	$28.9242	$28.92	$28.90	$28.90
Purchase #4	$165.33	3.645%	$171.3563	$171.36	$171.35	$171.40
Purchase #5	$162.64	8.566%	$176.5717	$176.57	$176.55	$176.60
Purchase #6	$82.54	8.124%	$89.2455	$89.25	$89.25	$89.20
Purchase #7	$187.54	7.668%	$201.9206	$201.92	$201.90	$201.90
7 purchase totals =	$738.08		$789.0764	$789.08	$789.00	$789.10