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	$80.41	3.125%	$82.9228	$82.92	$82.90	$82.90
Purchase #2	$81.92	7.492%	$88.0574	$88.06	$88.05	$88.10
Purchase #3	$82.90	9.676%	$90.9214	$90.92	$90.90	$90.90
Purchase #4	$179.36	8.226%	$194.1142	$194.11	$194.10	$194.10
Purchase #5	$30.25	10.774%	$33.5091	$33.51	$33.50	$33.50
Purchase #6	$111.92	7.191%	$119.9682	$119.97	$119.95	$120.00
Purchase #7	$165.69	13.524%	$188.0979	$188.10	$188.10	$188.10
7 purchase totals =	$732.45		$797.5910	$797.59	$797.50	$797.60