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	$247.84	3.336%	$256.1079	$256.11	$256.10	$256.10
Purchase #2	$142.88	5.637%	$150.9341	$150.93	$150.95	$150.90
Purchase #3	$75.95	8.365%	$82.3032	$82.30	$82.30	$82.30
Purchase #4	$119.71	12.459%	$134.6247	$134.62	$134.60	$134.60
Purchase #5	$57.71	4.260%	$60.1684	$60.17	$60.15	$60.20
Purchase #6	$20.50	3.530%	$21.2237	$21.22	$21.20	$21.20
Purchase #7	$56.67	5.368%	$59.712	$59.71	$59.70	$59.70
7 purchase totals =	$721.26		$765.0740	$765.06	$765.00	$765.00